# Theory of the American Twist Kick Serve

#### Dan R

##### Semi-Pro
I have never really been able to hit this serve, except by accident once in a blue moon. Part of the problem is that I've never seen a good explanation how you can get the ball to curve one way and bounce another. But I think I may have hit on something finally.

First, it probably helps to define the kind of serve I'm talking about. From a right hander's perspective it's a serve that moves from right to left in the air (like a slice serve), but bounces sharply up and to the right (unlike a slice serve that bounces to the left).

I was talking to an instructor about problems I have returning slice serves, and that the return goes too far cross court. I said I thought this was because I was too far out front on them. He said, maybe not, it might be because I'm improperly adjusting for the spin as it comes off the racket. Again, assuming we are talking right handers here, a slice serve is coming toward me curving to my right but once it hits my strings it will bounce to my left - cross court. So, If I don't take this into consideration then my return will go too cross court. I'd never heard this before, and was skeptical because as everyone knows a slice serve bounces to the the returners' right off the bounce, why would it go the other way when it hit's my racket?

Well, by tossing me balls with slice spin on them and letting them hit my racket he proved that he was right. I later verified this by hitting slice side spin at a wall and sure enough the ball goes sharply the other way when it hits the wall (if the ball is moving right to left in the air, it comes off the wall to the right - the more slice on the ball the more it goes to the right).

So, when a slice serve hits the ground it keeps going in the direction it was going in the air, but when it hits a wall or a racket it goes the opposite direction, and of course the opposite direction bounce is what an American twist kick serve does. Why is that?

It's the angle of incidence. If the ball hits the floor at a shallow glancing angle that does not take much spin off the ball, but when it hits the wall or a racket the impact is much more direct and the wall or racket grabs the ball and reverses the spin direction (that's my theory).

So, to hit the American twist serve the ball has to be dropping as nearly straight down as possible to turn the floor into a wall - more straight down than a slice serve. Seems like you can do this by hitting a ton of top and side spin, and/or hitting it high in the air so that gravity pulls it down more vertically. I have not tried this out yet, but I think I can see now how to hit the serve.

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#### travlerajm

##### Legend
You more or les got it.

A lot of people profess voodoo concepts like “hit up on the side of the ball to produce gyrospin” but this is bull****.

There is no voodoo or magic.

Just arch your back more and toss further to your left on your topspin slice serve so that the angle of attack on your topspin slice serve is more vertical, and less slice, and the spin will grab the ground more and bounce less left and more right. It’s pretty simple in concept, just hard for most people to execute consistently.

#### sureshs

##### Bionic Poster
An American Twist Serve (and I hit it occasionally by fluke, not intent) is a topspin serve with only a little amount of sidespin.

Let us first understand why a slice serve or a kick serve from a rightie server moves right to left in the air. It is because of sidespin, which causes a sideways Magnus effect in the same way as topspin causes a downward Magnus effect (one side ball linear movement is in the same direction as its spin movement increasing the speed, and on the other in the opposite direction decreasing the speed, and more speed = less pressure by Bernoulli's principle, and ball follows pressure gradient).

Then let us see what happens after bounce. In most cases, a spinning ball retains the direction of spin after bounce. In some cases like with extremely high friction, it can reverse direction. Another case is underspin or slice, which becomes topspin after bounce (a known fact which comes as a surprise to many). As I said, an American Twist serve has only a little sidespin as it is hit 8 to 2 or 7 to 1. A slice is hit more like at 3. Also, the slice serve does not always bounce left, especially if is a top-slice. Anyways, the axis of sidespin is the opposite (wrt vertical axis) between the regular slice and the AT. The slice has its axis NW to SE, while the AT has the axis NE to SW. Assuming no spin reversal on bounce, you can convince yourself that the ball will move left in the first case and right in the second.

Short answer: Magnus effect of sidespin before bounce, and preservation of sidespin axis direction after bounce.

D

#### Deleted member 23235

##### Guest
I have never really been able to hit this serve, except by accident once in a blue moon. Part of the problem is that I've never seen a good explanation how you can get the ball to curve one way and bounce another. But I think I may have hit on something finally.

First, it probably helps to define the kind of serve I'm talking about. From a right hander's perspective it's a serve that moves from right to left in the air (like a slice serve), but bounces sharply up and to the right (unlike a slice serve that bounces to the left).

I was talking to an instructor about problems I have returning slice serves, and that the return goes too far cross court. I said I thought this was because I was too far out front on them. He said, maybe not, it might be because I'm improperly adjusting for the spin as it comes off the racket. Again, assuming we are talking right handers here, a slice serve is coming toward me curving to my right but once it hits my strings it will bounce to my left - cross court. So, If I don't take this into consideration then my return will go too cross court. I'd never heard this before, and was skeptical because as everyone knows a slice serve bounces to the the returners' right off the bounce, why would it go the other way when it hit's my racket?

Well, by tossing me balls with slice spin on them and letting them hit my racket he proved that he was right. I later verified this by hitting slice side spin at a wall and sure enough the ball goes sharply the other way when it hits the wall (if the ball is moving right to left in the air, it comes off the wall to the right - the more slice on the ball the more it goes to the right).

So, when a slice serve hits the ground it keeps going in the direction it was going in the air, but when it hits a wall or a racket it goes the opposite direction, and of course the opposite direction bounce is what an American twist kick serve does. Why is that?

It's the angle of incidence. If the ball hits the floor it's at a shallow glancing angle that does not take much spin off the ball, but when it hits the wall or a racket the impact is much more direct and the wall or racket grabs the ball and reverses the spin direction (that's my theory).

So, to hit the American twist serve the ball has to be dropping as nearly straight down as possible to turn the floor into a wall - more straight down than a slice serve. Seems like you can do this by hitting a ton of top and side spin, and/or hitting it high in the air so that gravity lets it fall more vertically. I have not tried this out yet, but I think I can see now how to hit the serve.
i wouldn't think of the ball "dropping" as much as i would think about the path to contact.
ie. i can hit a kick/top/slice/flat off a dropping ball (ie. just toss it 2 ft above my contact).
question is, how can i swing "mostly up" (top/kick -typically just above or slightly to left of my head)
how can i swing "mostly across" (slice, topslice - typically to the right of my head).

technically bend your knees more (or bow at the hip)... arching your back is a recipe for injury. shoulde be keeping your back straight.

#### sureshs

##### Bionic Poster
You more or les got it.

A lot of people profess voodoo concepts like “hit up on the side of the ball to produce gyrospin” but this is bull****.

There is no voodoo or magic.

Just arch your back more and toss further to your left on your topspin slice serve so that the angle of attack on your topspin slice serve is more vertical, and less slice, and the spin will grab the ground more and bounce less left and more right. It’s pretty simple in concept, just hard for most people to execute consistently.
Actually, for most people the first problem is the toss. That is why they cannot consistently execute any further piece of instruction (all their lives).

#### travlerajm

##### Legend
I think the clock angle analogy sometimes throws people off because there exists a clock angle halfway between a slice serve and a twist serve that bounces straight. The server might think he’s serving a pure topspin serve and hitting nearly 6 to 12 due to the straight bounce. But in actuality his clock angle is somewhere around 8 to 2. Starting from this ‘faux topspin serve’ clock angle (that produces straight bounce), adjusting more toward 7 to 1 will make it bounce right, and adjusting more towards 9 to 3 will make it bounce more left.

#### sureshs

##### Bionic Poster
Did you know that an AT serve can be hit by a rightie from the deuce court? You don't, because this is the first time I am revealing this to the tennis world. Federer has a serve from the deuce court which I have seen moving in the air from the opponent's AD court into his (deuce) court, landing just to the left (as seen by the server) of the center line, and then taking off back towards the AD court (rightie returner's backhand) after bounce! This would usually be called a type of topslice, but think about it. It has the same physics as the AT serve from the AD court! The ball and the bounce area on the court don't care what it is called.

#### sureshs

##### Bionic Poster
I think the clock angle analogy sometimes throws people off because there exists a clock angle halfway between a slice serve and a twist serve that bounces straight. The server might think he’s serving a pure topspin serve and hitting nearly 6 to 12 due to the straight bounce. But in actuality his clock angle is somewhere around 8 to 2. Starting from this ‘faux topspin serve’ clock angle (that produces straight bounce), adjusting more toward 7 to 1 will make it bounce right, and adjusting more towards 9 to 3 will make it bounce more left.
Yes I think it is very difficult to hit 6 to 12 because the arm is on the right of the body, not on top of the head.

D

#### Deleted member 23235

##### Guest
I think the clock angle analogy sometimes throws people off because there exists a clock angle halfway between a slice serve and a twist serve that bounces straight. The server might think he’s serving a pure topspin serve and hitting nearly 6 to 12 due to the straight bounce. But in actuality his clock angle is somewhere around 8 to 2. Starting from this ‘faux topspin serve’ clock angle (that produces straight bounce), adjusting more toward 7 to 1 will make it bounce right, and adjusting more towards 9 to 3 will make it bounce more left.
lol, i feel like the clock analogy only made sense to me AFTER i learned how to serve. like a refernce guide for those who already know the formula.
but when i was learning... OMG i wanted to smash that clock so many times.

#### Dan R

##### Semi-Pro
Based on this, I think it makes sense to think of the AT serve as a slice serve that has a very high arc. You can get the arc by hitting it with a healthy amount of top spin, or just hit slow with a ton of slice spin but high up in the air. The slice serve that is flat at skidding will not twist. Can't wait to try this out now that I think I get what's going on.

The other thing this means is that you can spot the AT serve as a returner by paying attention to the arc. If it's high it's going to twist, if it's low and flat it's going to skid.

#### sureshs

##### Bionic Poster
Based on this, I think it makes sense to think of the AT serve as a slice serve that has a very high arc. You can get the arc by hitting it with a healthy amount of top spin, or just hit slow with a ton of slice spin but high up in the air. The slice serve that is flat at skidding will not twist. Can't wait to try this out now that I think I get what's going on.

The other thing this means is that you can spot the AT serve as a returner by paying attention to the arc. If it's high it's going to twist, if it's low and flat it's going to skid.
That is a very practical observation. A high serve means more topspin and less sidespin, which are the ingredients of the AT serve.

D

#### Deleted member 23235

##### Guest
Based on this, I think it makes sense to think of the AT serve as a slice serve that has a very high arc. You can get the arc by hitting it with a healthy amount of top spin, or just hit slow with a ton of slice spin but high up in the air. The slice serve that is flat at skidding will not twist. Can't wait to try this out now that I think I get what's going on.

The other thing this means is that you can spot the AT serve as a returner by paying attention to the arc. If it's high it's going to twist, if it's low and flat it's going to skid.
not sure what you mean by arc... but for me, if you're reading the serve by it's arc, it's too late... i typically look in this priority
1. toss and contact location
2. swing path
for me, the toughest to read is the flat vs. slice.
AT serves are pretty obvious

#### travlerajm

##### Legend
One way to think of it is to consider the angle of the spin axis relative to the ground. If the spin axis is vertical, the spin will not grab the ground, regardless of the horizontal speed when the ball hits the ground. This is because the spin is corkscrewing relative to the ground, as what happens on a pure slice serve.

On the other hand, if the spin axis is horizontal and the spin rate is very high, the spin will tend to grab the ground and cause the ball to rebound in the direction that the bottom surface of the ball is moving. This is what happens on a heavy topspin forehand.

A twist serve has the spin axis enough horizontal to grab the ground like a topspin forehand, but also enough vertical axis like a slice serve to give it sideways bend in the air. It is simply a hybrid of these two cases.

#### Dan R

##### Semi-Pro
not sure what you mean by arc... but for me, if you're reading the serve by it's arc, it's too late... i typically look in this priority
1. toss and contact location
2. swing path
for me, the toughest to read is the flat vs. slice.
AT serves are pretty obvious
I'm referring to the downward trajectory of the ball as it comes over the net. So, if the ball is coming in low and will glance off the court it won't twist, if the ball is coming more straight down into the court it will twist (assuming it's got slice on it).

I agree about the flat and slice, there's not a huge difference in the swing. Kick serves are pretty easy to spot.

#### Dan R

##### Semi-Pro
One way to think of it is to consider the angle of the spin axis relative to the ground. If the spin axis is vertical, the spin will not grab the ground, regardless of the horizontal speed when the ball hits the ground. This is because the spin is corkscrewing relative to the ground, as what happens on a pure slice serve.

On the other hand, if the spin axis is horizontal and the spin rate is very high, the spin will tend to grab the ground and cause the ball to rebound in the direction that the bottom surface of the ball is moving. This is what happens on a heavy topspin forehand.

A twist serve has the spin axis enough horizontal to grab the ground like a topspin forehand, but also enough vertical axis like a slice serve to give it sideways bend in the air. It is simply a hybrid of these two cases.

I agree, and would just add that not every serve with the proper slice and top spin combination will twist. It will also depend on the amount of forward momentum the ball has on it. Nadal hit's a great slice top spin serve that does not twist and that's because it's not dropping straight down enough. It's got a lot of pace on it and a fairly low trajectory. If you can get to really drop like a sinker ball in baseball then it will twist.

#### travlerajm

##### Legend
I agree, and would just add that not every serve with the proper slice and top spin combination will twist. It will also depend on the amount of forward momentum the ball has on it. Nadal hit's a great slice top spin serve that does not twist and that's because it's not dropping straight down enough. It's got a lot of pace on it and a fairly low trajectory. If you can get to really drop like a sinker ball in baseball then it will twist.
It's possible to hit a twist serve with very high speed (greater than 100mph). The reason Nadal's topspin-slice serve doesn't twist has more to do with the clock angle - he is attacking the ball (if he were righty) at about 8:30 to 2:30 (nearly pure slice, or about 15 degrees relative to the ground). If his swingpath was more vertical (say about 7:30 to 1:30, or about 45 degrees relative to the ground), it would kick in the opposite direction, as it would be an AT serve. Most serves are hit somewhere in the middle between these two cases (about 8 to 2 clock angle, or about 30 degrees relative to the ground), due to the geometry of the arm relative to the body when you are standing, as Sureshs mentioned above. It's unnatural and even uncomfortable for some people to bend backward enough to hit a serve with the 7:30 to 1:30 (45 deg angle) swingpath required for an effective AT serve.

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#### Chas Tennis

##### Legend
I don't know what the American Twist serve is. I have been looking for high speed videos of how the racket impacts the ball, none yet.

1) The Tennis Warehouse article, "The Physics of the Kick Serve" by Rod Cross describes the kick serve in detail. Suggest that you make a paper copy and use a highlighter to locate several important points that are spread here and there throughout this article. You could also move the article to WORD and mark the important passages for reading on your computer.
http://twu.tennis-warehouse.com/learning_center/kickserve.php

Note - The racket head orientation in Figure 1 of The Physics of the Kick Serve is not correct. The racket cannot rise from the orientation shown. The racket impacts the ball while the wrist is still increasing the forearm to racket shaft angle.

2) The book Technical Tennis, Cross & Lindsay, has clear pictures of the location on the ball that the racket contacts. The pictures show a sphere and therefore give the 3 dimensional information that is always missing in misleading 2D 'clock face' descriptions.
http://twu.tennis-warehouse.com/learning_center/kickserve.php

3) The spins on the ball for the Kick, Flat and Slice serves were described for elite female servers. This publication is the best one that I have found and has the 'tell all' picture of the tennis ball spin. It indicates these unexpected facts:
1. The kick serve has more side spin component than top spin component to its spin vector.
2. The kick serve has more side spin component than the slice serve.
3. The flat, slics and kick serves all have side spin components, top spin components and 'spiral spin' components. If you think in terms of only two components - side spin component and top spin component you can never understand the ball spin.

4) I have posted a few high speed videos clearly showing how the kick serve impacts the ball; 1) from the view behind and 2) from the view to the side of the server. These show the racket rising and that the face of the racket is more closed just before impact.

All the above sources of information are consistent with high speed videos of the racket direction and tilt of kick serve impacts.

There are not enough high speed videos - available by internet search - showing the racket details before, during and after impact for the kick serve. I hope that some posters can show more links showing high speed video closeups of the impact for the kick serve. And especially for the American Twist. Useful high speed videos of racket impacts for each type are rare and have to contain references for forward and show the vertical as well as a confirmed kick serve bounce of the ball.

There are also few videos of the top spin serve where, I believe, the upward racket motion will appear in videos to be very similar to the kick serve but the racket will first contact close to the rear of the ball and not as much on the top half of the ball as Technical Tennis indicates. Who knows about the American Twist serve?

Misunderstandings

I read somewhere that the gyrospin component caused the side bounce of the kick serve (Cross TW article?) . I believe that is true.

But for a few years, I misunderstood and thought that if a serve had gyrospin and would bounce to the side, that meant that the kick serve had more gyrospin than the slice or flat serves. But look carefully at the ball spin vector picture and you will see that all three types of serves have very considerable gyrospin.

Also, the term gyrospin component might not the best term because for a few years I muddle thought that gyrospin was somehow special in causing the gyroscopic effect. The gyroscopic effect does cause the ball's spin axis to remain the same during its flight to the bounce. But there is nothing special about the gyrospin component, it's the same as the Top Spin component and Side Spin component, all components describe the one spin axis.

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#### FiReFTW

##### Legend
They are all kick serves, twist serve is a made up thing.

#### travlerajm

##### Legend
There is negligible spiralspin component in any tennis shot at the moment of impact. This is a made-up thing. The AT, however is real.

Due to the laws of physics, a tennis racquet can only contact one side of the ball at one time, with a velocity vector pointing in a single direction.

#### Chas Tennis

##### Legend
All spins are 3D and very incorrectly described by the terms
Top Spin Serve
Side Spin Serve

...........................................

A lot of tennis terminology is not very accurate and worse, if you try to interpret the word as meaningful, it can be misleading.

Here is the simplest thing - the spin axes on flat, slice and kick serves - and one of the few available spin measurements. This is the best work that I am aware of and I also have not seen similar measurements for ground strokes.

https://www.researchgate.net/public...e_tennis_serve_Spin_rate_and_axis_of_rotation

For those who want to go into these measurements in detail -

As Rod Cross said, a ball has only one spin axis. The direction of that spin axis can be described with 3 components as is done with vectors.

For the kick serve the spin axis vector is shown as a grey dashed line and the components of it are AVx, AVy, and AVz as labeled.

If a ball had only side spin, the spin axis AVz would be the only spin component.

If a ball had only topspin, the spin axis AVy would be the only spin component.

If a ball had only gyrospin, the spin axis AVx would be the only spin component. (This is the spin of a well thrown American Football 'bullet' pass.)

The picture above shows the actual spin axis components that have been measured for some high level serves.

Kick serve - AVz>AVy>AVx (means AVz is greater than AVy is greater than AVx.) This says that the sidespin component of a kick serve is greater than the topspin component! But I thought the Topspin component would be the greater!! Also the sidespin component is larger than the sidespin component of the slice serve!! The gyrospin component is only slightly greater than the gyrospin components of the slice and flat serves.

Slice serve- AVz > AVy > AVx. This means that the sidespin component is the largest as we would expect. The gyrospin component is close to that of the kick serve and flat serves.

Flat serve - AVz > AVz = AVx. This means that the sidespin component is larger than the topspin or gyrospin components. But the gyropspin component is also close to that of the slice and kick serves.

As I interpret the Cross and Lindsay reference, Technical Tennis, the "Top Spin" serve is similar to the kick serve except that the kick serve has more gyrospin. The gyrospin accounts for the sideward bounce of the kick serve.

The above is a full 3D description of the spin axes magnitudes and directions. If you want reliable and clear information on spins try and find similar measurements.

https://www.researchgate.net/public...e_tennis_serve_Spin_rate_and_axis_of_rotation

Abstract
Abstract
The purpose of this study was to describe three-dimensional ball kinematics including spin axis and spin rate for the flat, slice, and kick serves executed by elite male tennis players. Trajectories of three retro-reflective markers attached to the surface of the ball were measured using a Vicon MX motion analysis system. The local coordinate system of the ball enabled the ball's angular velocity vector to be determined. Mean (+/- SD) spin rates recorded were 127.4 (+/- 56.3), 232.1 (+/- 34.8), and 336.5 (+/- 51.5) rad/s for the flat, slice, and kick serves, respectively. The resultant horizontal velocities of the ball were 52.0 (+/- 2.9), 46.4 (+/- 3.4), and 40.8 (+/- 2.8) m/s, respectively, and a clear tradeoff existed between the development of ball spin rate and horizontal ball velocity, with resultant horizontal velocities of 52.0 (+/- 2.9), 46.4 (+/- 3.4), and 40.8 (+/- 2.8) m/s, respectively, being recorded. The spin axis and ball velocity vector were close to perpendicular regardless of serve type. Mean angles between the spin axis and the horizontal plane (elevation angles) were 65.6 degrees (+/- 10.2 degrees), 68.4 degrees (+/- 6.9 degrees), and 54.5 degrees (+/- 8.4 degrees) for the flat, slice, and kick serves, respectively.

#### Dan R

##### Semi-Pro
All spins are 3D and very incorrectly described by the terms
Top Spin Serve
Side Spin Serve

...........................................

A lot of tennis terminology is not very accurate and worse, if you try to interpret the word as meaningful, it can be misleading.

Here is the simplest thing - the spin axes on flat, slice and kick serves - and one of the few available spin measurements. This is the best work that I am aware of and I also have not seen similar measurements for ground strokes.

https://www.researchgate.net/public...e_tennis_serve_Spin_rate_and_axis_of_rotation

For those who want to go into these measurements in detail -

As Rod Cross said, a ball has only one spin axis. The direction of that spin axis can be described with 3 components as is done with vectors.

For the kick serve the spin axis vector is shown as a grey dashed line and the components of it are AVx, AVy, and AVz as labeled.

If a ball had only side spin, the spin axis AVz would be the only spin component.

If a ball had only topspin, the spin axis AVy would be the only spin component.

If a ball had only gyrospin, the spin axis AVx would be the only spin component. (This is the spin of a well thrown American Football 'bullet' pass.)

The picture above shows the actual spin axis components that have been measured for some high level serves.

Kick serve - AVz>AVy>AVx (means AVz is greater than AVy is greater than AVx.) This says that the sidespin component of a kick serve is greater than the topspin component! But I thought the Topspin component would be the greater!! Also the sidespin component is larger than the sidespin component of the slice serve!! The gyrospin component is only slightly greater than the gyrospin components of the slice and flat serves.

Slice serve- AVz > AVy > AVx. This means that the sidespin component is the largest as we would expect. The gyrospin component is close to that of the kick serve and flat serves.

Flat serve - AVz > AVz = AVx. This means that the sidespin component is larger than the topspin or gyrospin components. But the gyropspin component is also close to that of the slice and kick serves.

As I interpret the Cross and Lindsay reference, Technical Tennis, the "Top Spin" serve is similar to the kick serve except that the kick serve has more gyrospin. The gyrospin accounts for the sideward bounce of the kick serve.

The above is a full 3D description of the spin axes magnitudes and directions. If you want reliable and clear information on spins try and find similar measurements.

https://www.researchgate.net/public...e_tennis_serve_Spin_rate_and_axis_of_rotation

Abstract
Abstract
The purpose of this study was to describe three-dimensional ball kinematics including spin axis and spin rate for the flat, slice, and kick serves executed by elite male tennis players. Trajectories of three retro-reflective markers attached to the surface of the ball were measured using a Vicon MX motion analysis system. The local coordinate system of the ball enabled the ball's angular velocity vector to be determined. Mean (+/- SD) spin rates recorded were 127.4 (+/- 56.3), 232.1 (+/- 34.8), and 336.5 (+/- 51.5) rad/s for the flat, slice, and kick serves, respectively. The resultant horizontal velocities of the ball were 52.0 (+/- 2.9), 46.4 (+/- 3.4), and 40.8 (+/- 2.8) m/s, respectively, and a clear tradeoff existed between the development of ball spin rate and horizontal ball velocity, with resultant horizontal velocities of 52.0 (+/- 2.9), 46.4 (+/- 3.4), and 40.8 (+/- 2.8) m/s, respectively, being recorded. The spin axis and ball velocity vector were close to perpendicular regardless of serve type. Mean angles between the spin axis and the horizontal plane (elevation angles) were 65.6 degrees (+/- 10.2 degrees), 68.4 degrees (+/- 6.9 degrees), and 54.5 degrees (+/- 8.4 degrees) for the flat, slice, and kick serves, respectively.
We had this discussion before but this diagram is clearly wrong. The kick serve can't have more side spin on it than a slice serve. So, something is not matching up here.

#### Dan R

##### Semi-Pro
They are all kick serves, twist serve is a made up thing.
This doesn't look made up. I think you can see in this example the serve is going very directly into the ground with slice spin on it, which cause the twist on the bounce.

#### Chas Tennis

##### Legend
There is negligible spiralspin component in any tennis shot at the moment of impact. This is a made-up thing. The AT, however is real.....
Did someone say anything about "moment of impact"? Quoting the source often avoids misinterpretations?

..........
Due to the laws of physics, a tennis racquet can only contact one side of the ball at one time, with a velocity vector Editpointing in a single direction.
The racket just before first touch has an angle to its face and that alone will determine exactly where first contact on the ball will be. Try it with a ball and racket. Fortunately, that racket face angle can be seen in high speed videos and can tell us where first contact on the ball will be. For example, if the racket string face is closed, first contact will be on the top half of the ball (important for the kick serve).

After first contact, the strings and ball distort so much that it is impossible to describe 'direction' in a few words.

I vote that we leave impact descriptions to tennis reseachers because of difficulty.

..........
Due to the laws of physics, a tennis racquet can only contact one side of the ball at one time, with a velocity vector pointing in a single direction.
"Velocity vector" of what and when?

The spin vector of the ball as in the picture is in 3D space so
1) a vertical component, AKA 'side spin'
2) a horizontal component, AKA 'top spin'
3) a forward component, AKA 'gyrospin' or 'spiral spin',
are necessary components to describe the spin vector in 3 dimensions. Those 3 components are what the picture with the ball shows for each type of serve.

I read somewhere that the gyrospin component caused the side bounce of the kick serve. For a few years, I misunderstood and believed that if a serve had gyrospin and bounced to the side it also meant that the kick serve had more gyrospin than the slice or flat serves. But look carefully the the ball picture and you will see that all three types of serve have very considerable gyrospin. More on this was added to post #18.

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#### Hmgraphite1

##### Hall of Fame
It seems complicated, there is that one super high frame rate video showing the ball is hardly round coming off the racquet as it's walls bounce in and out deforming its shape.
I thought the twist had a swing path from 5 to 11 for righties?

#### Chas Tennis

##### Legend
We had this discussion before but this diagram is clearly wrong. The kick serve can't have more side spin on it than a slice serve. So, something is not matching up here.
These measurements were for elite female servers. I believe that they are representative for the types of serves. I would like to see similar measurements for current ATP servers.

Before writing off the ball spin diagram keep in mind that the authors are leading tennis researchers that can measure spins and have done so for years.

Read Cross's article. I believe that he may mention some of what is seen in the ball spin vector diagrams. Cross also measures spins.

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#### Chas Tennis

##### Legend
It seems complicated, there is that one super high frame rate video showing the ball is hardly round coming off the racquet as it's walls bounce in and out deforming its shape.
I thought the twist had a swing path from 5 to 11 for righties?
The clock face is so simple and familiar. 2D

The tennis serve is so complicated. The racket face center moves on a 3D path while at the same time the face is rotating around more than two axes.............

Do you believe "5 to 11" can describe the serve swing path?

If the racket is closed at first contact with the ball, the racket strings contact on the upper half of the ball.
If the racket is open at first contact with the ball, the racket strings contact on the lower half of the ball.

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#### sureshs

##### Bionic Poster
Professor Chas Tennis to the rescue!

##### Legend
lol, i feel like the clock analogy only made sense to me AFTER i learned how to serve. like a refernce guide for those who already know the formula.
but when i was learning... OMG i wanted to smash that clock so many times.
Yeah. Is the clock face supposed to be referenced laid down on the ground or propped upright vertically or seen looking up? Hard to know exactly when you don’t understand how to serve.

Just give me the digital watch so I don’t have to make my own interpretation!

#### travlerajm

##### Legend
If you read the text of the Cross abstract closely, it is stating that gyrospin is negligible compared to topspin and sidespin. Hmm.

#### Hmgraphite1

##### Hall of Fame
The clock face is so simple and familiar. 2D

The tennis serve is so complicated. The racket face center moves on a 3D path while at the same time the face is rotating around more than one axis.............

Do you believe "5 to 11" can describe the serve swing path?

If the racket is closed at first contact with the ball, the racket strings contact on the upper half of the ball.
If the racket is open at first contact with the ball, the racket strings contact on the lower half of the ball.
I know your point and agree, but it's a feel thing description of the racquet path irregardless of the actual impact to the ball. But I need to experiment some more just relaying my understanding at this point.

#### coupergear

##### Professional
They are all kick serves, twist serve is a made up thing.
not quite. the dude in the video is correct. the only difference between a American twist and a Kick is that the AT you follow through on your same side and back behind which is kind of an awkward finish as opposed to curling around across your front. Both generate kick. The AT was an earlier iteration. Both FTs are kind of tacked on because the racket is moving out and away from your body laterally.. Doesn't really naturally FT on either side but you can't let whack your leg!!

#### travlerajm

##### Legend
This guy says to hit the inside of the ball more to get that crazy bounce.
This "hit the inside of the ball" thing has been around for more than 30 years, perpetuated by lifelong tennis pros with no background in physics fundamentals.

#### Chas Tennis

##### Legend
I just found a video searching on the American Twist Serve and it was what I would call a kick serve. For me the Kick Serve = bounce high to the right. The server in an instructional video thought differently, he said that the American Twist Serve bounced high to the right and the kick serve was something. He showed the racket oriented moving as my kick serve videos do as viewed from behind.

There are a variety of usages for the terms

Top Spin serve
Kick Serve
American Twist Serve

When I first heard the term American Twist Serve it was about 1980 or so. At that time for he American Twist it was often said that the American Twist was hard on your back and might cause injury.

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#### IowaGuy

##### Hall of Fame
What would y'all consider this 2nd serve by Rafter at 0:30?

#### Hmgraphite1

##### Hall of Fame
What would y'all consider this 2nd serve by Rafter at 0:30?

It doesn't "kick to the left" so topspin , just kicks up. Twist serve changes direction in a pretty major way on impact

#### Chas Tennis

##### Legend
The first Google find, a New York Times article, said that the bounce was to the "left" of the receiver. It is to the right as seen by the server.
https://straightsets.blogs.nytimes.com/2009/09/08/the-art-of-the-kick-serve/

It is difficult to judge the bounce for a kick serve if the camera is not looking along the trajectory at the bounce. From the server's good viewpoint the kick serve ball curves to the left in flight, as for a slice serve, and bounces to the right.

For the racket of the second Rafter serve (kick?) I don't see the racket rise much after impact. ? Look at impact and the frame after. Is that an affect of the camera's looking up? Repeat. The camera is looking down the court center line and that is not ideal for seeing the small angle bounce to the right. Better camera angle would be looking along the trajectory near impact. I'd say that there might be a little bounce to the right. ? Repeat.

The amount of bounce to the right probably depends on:
1) The spin rate (the length of the arrows in the ball spin picture are proportional to spin rate)
2) The angle of incline of the spin axis to the court surface at impact.
3) The speed of the ball's felt at the location of the ball contacting the court. (the kick serve's spin axis has a a greater tilt from the court surface and therefore the speed of the felt is higher than for the flat or slice serves).
4) The kick serve also impacts the court coming down at a sharper angle and therefore the ball will deform more because of the court surface.
5) The flat and slice serves have more grazing impact angles. The flat and slice serves have spin axes that are more normal to the court surface. Therefore the ball's felt that contacts the court is much closer to the spin axis and therefore the felt of the flat and slice serves have a slower speed than the felt of the kick serve.

Demo - Drill two holes through the center of a tennis ball and and stick a pencil through them. The pencil represents the spin axis. Spin the ball like a top tilted like the spin axes in the ball spin picture. Tilt the pencil to a surface and notice that the felt meeting the surface has a higher velocity as the pencil is tilted to the surface. With spin axis tilt the point of contact moves out from spin axis where the felt velocity becomes higher. The spin axis stays in the same direction from racket impact to the court bounce due to the gyroscopic effect. (the gyroscopic effect has nothing special to do with the gyrospin component of the spin vector).

I posted on this subject with pictures roughly 2 years ago.

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#### travlerajm

##### Legend
What would y'all consider this 2nd serve by Rafter at 0:30?

That’s what most people refer to as a ‘topspin’ serve or a ‘kick’ serve. It’s also probably the most common type of serve. The swingpath is roughly 8 to 2 across the back of the ball. The spin is actually a lot more slice than top, but it has enough topspin component to grab the ground and kick straight rather than kicking to the left like it would if it was more pure slice. It doesn’t have enough of a topspin component to kick right like an AT.

#### Hmgraphite1

##### Hall of Fame
The first Google find of a New York Times article said that the bounce was to the "left". In the NYT article itself, it said that the bounce was to the left for the receiver.

It is difficult to judge the bounce for a kick serve if the camera is not looking along the trajectory at the bounce. From the server's good viewpoint the kick serve ball curves to the left in flight, as for a slice serve, and bounces to the right. For the racket of the second Rafter serve (kick?) I don't see the racket rise much after impact. ? Look at impact and the frame after. Better camera angle would be along the trajetory The camera is looking down the court center line and is not ideal for seeing the bounce. I'd say that there is a little bounce to the right. ?

The amount of bounce to the right probably depends on:
1) The spin rate (the length of the arrows in the ball spin picture are proportional to spin rate)
2) The angle of incline of the spin axis to the court surface at impact,
3) The speed of the ball's felt at the location of the ball contacting the court. (the kick serve's spin axis has a a greater tilt from the court surface and therefore the speed of the felt is higher than for the flat or slice serves).
4) The kick serve also impacts the court coming down at a sharper angle and therefore the ball will deform more because of the court surface.
5) The flat and slice serves have more grazing impact angles. The flat and slice serves have spin axes that are more normal to the court surface. Therefore the ball's felt that contacts the court is much closer to the spin axis and therefore the felt of the flat and slice serves have a slower speed than the felt of the kick serve.

Demo - Drill two holes through the center of a tennis ball and and stick a pencil through them. The pencil represents the spin axis. Spin the ball like a top tilted like the spin axes in the ball spin picture. Tilt the pencil to a surface and notice that the felt meeting the surface has a higher velocity as the pencil is tilted to the surface. The spin axis stays the same from racket impact to the bounce.

I posted on this with pictures maybe 2 years ago.
Thanks for clarifying, I don't know lft from rt anymore, just take me out back and shoot me. Agree 2nd serve does kick a little to servers right. As a returner i've experienced up close maybe a one foot kick. Combine this with the slice it appeared to have and expecting it to be a foot over to the returners right, gives a two foot gap to scramble for.

#### onehandbh

##### Legend
That’s what most people refer to as a ‘topspin’ serve or a ‘kick’ serve. It’s also probably the most common type of serve. The swingpath is roughly 8 to 2 across the back of the ball. The spin is actually a lot more slice than top, but it has enough topspin component to grab the ground and kick straight rather than kicking to the left like it would if it was more pure slice. It doesn’t have enough of a topspin component to kick right like an AT.
I think the 2nd serve he hit has some “twist.”

If you look at the flight path of the ball as it approaches the court, it is curving slightly to the right from receiver’s POV, but after the bounce it goes a bit left instead of continuing in the same direction.

#### travlerajm

##### Legend
I think the 2nd serve he hit has some “twist.”

If you look at the flight path of the ball as it approaches the court, it is curving slightly to the right from receiver’s POV, but after the bounce it goes a bit left instead of continuing in the same direction.
That's why it was Rafter's (and most serve-and-volleyers') go-to serve. A slight variation in swingpath, using the same toss, can make the bounce kick either slightly to the right, or slightly to the left. It's how I used to serve when my style was pure serve-and-volley like Rafter's. I'd get a lot of free points in doubles from returners framing balls, and in singles the returner would have to stand at least 4 feet behind the baseline in order to hit it cleanly, which makes it easier to close the net. And this serve can be hit with a lot more pace more naturally than a more extreme twist swingpath, because it doesn't require contortion of the body.

#### Keendog

##### Semi-Pro
Ask Holcombe Ward. He invented it, in 1897.

Sorry could only find Bill Tilden: (~7:00)

The only time I've heard people try and draw a differentiation between the twist and kick serve is on here. They have always just been interchangeable terms for mine.

D

#### Deleted member 23235

##### Guest
I think the 2nd serve he hit has some “twist.”

If you look at the flight path of the ball as it approaches the court, it is curving slightly to the right from receiver’s POV, but after the bounce it goes a bit left instead of continuing in the same direction.
+1

when I “twist” to deuce side it follows that type of path (right to left curve + straight bounce). to me the “change in direction” is not measured off the bounce but measured as a difference of the right to left curve and it’s “expected bounce” (which on a slice would normally break much more to the left)

kicker to ad side is typically more dramatic off the bounce

my topspin serve would have less/no right to left curve (so folks wouldn’t expect it to break in any direction)

Sent from my iPhone using Tapatalk

#### Chas Tennis

##### Legend
Ask Holcombe Ward. He invented it, in 1897.

Looking for Holcomb Ward I found this
https://en.wikipedia.org/wiki/Serve_(tennis)

Kick/topspin/American twist/Reverse kick
Holcombe Ward and Dwight Davis introduced the kick/American twist serve in the late 1800s. The kick (or topspin) serve is generated by tossing the ball over the head, then hitting it laterally on the server's non-dominant side brushing upward toward the dominant side. When hit correctly, the ball clears the net in a high arc with heavy topspin, causing the ball to dive into the service box. Upon hitting the surface of the court, the ball may bounce high directly toward the receiver for a kick serve, or to the left for the receiver for an American twist serve. The physics of the spinning ball in flight involves the Magnus effect because the spinning ball creates a whirlpool of air around itself. The twist serve is a more extreme version of the kick serve, which involves more brushing of the ball from the 7–8 o'clock position to the 1–2 o'clock position, and faster swing speeds. If performed exceptionally, it can completely change the direction of the ball movement away from the other player, although this requires a very strong and flexible back.

Kick/topspin serves are often used as both first and second serves. As a first serve, a player will put more pace on the ball, while it is a consistent second serve since the spin brings it into the service box with high net clearance.

The reverse kick/American twist serve is rarely used except as a novelty. As the word "reverse" is defined, one must hit opposite to the side and opposite to the path of the kick struck serve.[clarification needed]

I'd like to have some references on these points. They also seem a little inconsistent.

"Upon hitting the surface of the court, the ball may bounce high directly toward the receiver for a kick serve, or to the left for the receiver for an American twist serve."

"The reverse kick/American twist serve is rarely used except as a novelty."

Is the reverse kick/American twist a different serve than the American Twist? Or is "reverse kick" another word for American Twist?

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What is the term usage usage by knowledgeable tennis players?

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Here is my video definition of a kick serve -

The bounce is more to the right than a continuation of the in flight trajectory and high. Note the receiver going high to reach the ball.
The path of the racket is caused by the forearm to racket angle still causing the center of the racket to rise. For the slice and flat serves the forearm to racket angle is larger due to wrist joint angular motions. ISR is also occurring at this time.

The camera is high and views along the trajectory and shows the bounce. A very good arrangement for any serve especially the kick serve.

To do single frame on Vimeo, click Vimeo, full screen, and hold down the SHIFT KEY while pressing the ARROW KEYS.

A second camera view from the side shows that the racket face is more closed just before impact, about 15 d from vertical than the slice or flat serves.

A USTA player had an exceptional high bouncing serve that I assumed was a kick serve. I asked him to serve to use high speed video to observe the details of his serve. One camera at 240 fps was on the racket and arm trying to observe how closed the racket face was and another camera at 60 fps from behind looking along the trajectory in order to to see the bounce to the right to identify the kick serve.

When I viewed the trajectory and bounce camera nearly all had very high bounces. Only three could be seen to bounce to the right (of the trajectory projected). I was very disappointed that most were not kick serves.

When I looked at the close up camera to observe how closed the racket face was just before ball impact I could not find the 15 d or so that I expected.

I believe that I was observing Top Spin serves with side spin component and top spin component and very little gyrospin component.

When I have again the opportunity video to someone with a confirmed kick serve that bounces to the right I would will try to observe the closed racket face at the instant before impact. To see this for a serve (right hand server) to the deuce court, place the camera about one step into the court from the baseline on the left sideline. You want the camera viewing perpendicular to the ball's trajectory at impact. Adjust camera position to see the racket edge just before impact. (Ideally you would see the closer edge blocking the far edge.) Racket tllted or not when the serve kicks to the right?

If you have a strong kick serve and a high speed video camera with small motion blur I'll be glad to talk you through taking the videos. These video observations would be very useful feed back for improving an existing kick serve.

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#### 5point5

##### Professional
I have never really been able to hit this serve, except by accident once in a blue moon. Part of the problem is that I've never seen a good explanation how you can get the ball to curve one way and bounce another. But I think I may have hit on something finally.

First, it probably helps to define the kind of serve I'm talking about. From a right hander's perspective it's a serve that moves from right to left in the air (like a slice serve), but bounces sharply up and to the right (unlike a slice serve that bounces to the left).

I was talking to an instructor about problems I have returning slice serves, and that the return goes too far cross court. I said I thought this was because I was too far out front on them. He said, maybe not, it might be because I'm improperly adjusting for the spin as it comes off the racket. Again, assuming we are talking right handers here, a slice serve is coming toward me curving to my right but once it hits my strings it will bounce to my left - cross court. So, If I don't take this into consideration then my return will go too cross court. I'd never heard this before, and was skeptical because as everyone knows a slice serve bounces to the the returners' right off the bounce, why would it go the other way when it hit's my racket?

Well, by tossing me balls with slice spin on them and letting them hit my racket he proved that he was right. I later verified this by hitting slice side spin at a wall and sure enough the ball goes sharply the other way when it hits the wall (if the ball is moving right to left in the air, it comes off the wall to the right - the more slice on the ball the more it goes to the right).

So, when a slice serve hits the ground it keeps going in the direction it was going in the air, but when it hits a wall or a racket it goes the opposite direction, and of course the opposite direction bounce is what an American twist kick serve does. Why is that?

It's the angle of incidence. If the ball hits the floor at a shallow glancing angle that does not take much spin off the ball, but when it hits the wall or a racket the impact is much more direct and the wall or racket grabs the ball and reverses the spin direction (that's my theory).

So, to hit the American twist serve the ball has to be dropping as nearly straight down as possible to turn the floor into a wall - more straight down than a slice serve. Seems like you can do this by hitting a ton of top and side spin, and/or hitting it high in the air so that gravity pulls it down more vertically. I have not tried this out yet, but I think I can see now how to hit the serve.
How do you hit an American Twist by accident?

#### TnsGuru

##### Professional
Is this what is desired when hitting this type of serve? when the ball lands towards the add corner and jumps towards the alley? Can this be aimed down the middle and have it kick and jam the player? I can hit topspin serves pretty much anywhere on the box but I don't think I ever had the ball jump away after landing but only on ocassion.

Obviously you have to hit a certain axis to create the spin but do some players contort or adust their wrist before and during contact into pronation to accentuate this action? Seems like the wrist action is too hard for me to detect when watching these videos even when the video speed is reduced.

This video is more about bouncing the ball over a barrier to improve bounce height after landing. The hips are more engaged and seems very effective. Big difference in before/after.

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#### Chas Tennis

##### Legend
Tennis Serve & Return Tips : American Twist Serve in Tennis - YouTube
See especially the serve at 1:10.

This serve is what I would call a kick serve. It curves to the left in flight and the bounce goes high and to the right. See 1:18 for the best one.

There is no way to actually hit straight up the back of the ball as in the demo at 0:23 using a service motion. And he was not say that there was. At 0:32 he says to hit with a combination of top spin and side spin and demos the racket rotating up at the hand. That demo resembles how the racket moves up during the kick serve. But see high speed videos for the real motion. See post #45 and the frames before, during and after impact.

#### travlerajm

##### Legend
Tennis Serve & Return Tips : American Twist Serve in Tennis - YouTube
See especially the serve at 1:10.

This serve is what I would call a kick serve. It curves to the left in flight and the bounce goes high and to the right. See 1:18 for the best one.

There is no way to actually hit straight up the back of the ball as in the demo at 0:23 using a service motion. And he was not say that there was. At 0:32 he says to hit with a combination of top spin and side spin and demos the racket rotating up at the hand. That demo resembles how the racket moves up during the kick serve. But see high speed videos for the real motion. See post #45 and the frames before, during and after impact.
This is a more technically correct and simpler way to teach it than to tell someone to “hit the inside part of the ball.”