@PKorda
I’m glad I made this video for you as funnily enough I noticed watching it that I myself don’t do what I’m telling you to do!
One of the three tips that I mention: low contact point so that your racket can continue going up after contact which is crucial in terms of being able to brush the ball up and to the side. Apparently I’m hitting the ball pretty much at the end of my reach hence ending up hitting more of a slice serve rather than a proper kicking one.
Anyway I just wanted to demonstrate my points. Especially the progression exercise at the beginning holding the racket pretty close to its throat is quite helpful imo. Give it a go.
I have said that the contact is "lower" but that needs more qualifications regarding the absolute height.
For a kick serve, the racket head strings must be rising while impacting the ball for adding the top spin to the kick serve.
Impacting the ball before the racket has reached its peak is necessary.
This is observed in high speed videos.
But that rising can be performed at various heights that are not necessarily 'lower' in actual height.
How can we impact the ball while the strings are still rising? Here are 3 different ways to do it.
1)
Lower Height of Impact Relative to Flat or Slice Serves. Use the same ISR service motion and jump and let the ball fall down roughly 6"? lower than for a slice or flat serve.
2)
Raise Racket Height Path Relative to Flat or Slice Serves. Use a similar ISR service motion, but instead of having the arm tilt to the side as for a flat or slice serve, have the arm more vertical and hit the ball more above your head. This might tend to retain the same ISR motion but impact the racket before it has risen near peak. The absolute height would be higher than for #1. The arm is observed in videos to be more vertical for the kick serve and the ball is impacted above the head.
3)
Raise Racket Height Path Relative to Flat or Slice Serves. Jump higher and use the same service motion that the part of the motion with the rising racket is elevated. The absolute height for impact may be the same as for a flat or slice serve.
The ball impact
relative to the ISR motion racket path has to be lower, but relative to absolute height there are options from jumping height and arm angle. Some players may jump higher and elevate the ISR racket head path. Others may make their arm more vertical, and others may let the ball fall down farther. Each individual server may be different. ? (Note - when the racket is still rising it also is pointing more to the left. To align the racket face for impact the chest points more to the side as seen in videos from above. That seems to be what is going on. ? )
To make sense out of this for the ATP pros you would have to have many measurements of how various players hit confirmed kick serves.
To illustrate some of these points here is how an individual server adjusts for a kick or slice serve. Toly GIFs.
Look at the arm angle and the actual height of impact (relative to the net). The racket peak is not quite shown but it is approaching the base line as a reference. Notice the forearm-to-racket-shaft angle at impact. Distance on my screen between net and ball 7 mm.
Look at the actual height of impact relative to the net and the racket's peak height. Look at the arm tilt angle. Notice the forearm-to-racket-shaft angle at impact. Distance on my screen between net and ball 16 mm.
From this comparison the player appears to have elevated the arm for the kick serve and let the ball drop down farther for impact. The forearm to racket shaft angle has to present and used, so it is not an option for adjusting height. We don't have statistics for other players or additional measurements for this player. The two videos were taken with similar camera angles so these comparisons are pretty accurate.
If we were observing the angular rotation of ISR from start to impact we might find that it is less for the kick serve and that is maybe why the chest has to be more turned to the right at impact - to get the correct right-left aim.