Bye, from 10:00 onward in this mixed-clips Fed video...
for example at 10:08, you'll see that just into the hit Fed lifts his off arm forearm just a bit. It's practice, he's coasting. If you have any match tapes you can see him lift it in earnest. (Better yet, you should try it racquet in hand.) Players who were shamelessly aggressive with their off-arm swing, pull-in, and then forearm lift are Sharapova, James Blake, and in his own way, Lendl. Lendl would do the off-arm pull in by looping his fairly straight arm down in toward his leg (to grab the arm's momentum) and then lift the arm rightward and up. Try it sometime. It actually works very smoothly.
I think JY went over the question of how much a particular grip affects how much people need to lag their wrist. I have a different view because I have a more limited experience. If you, Bye, get ready for the next hit to come over the way Fed does, and if you therefore turn to hit a forehand the way he does (just meaning unit turn, racquet head high, grip lower, but racquet generally fairly vertical, then you, like Fed, will have your wrist bent back already a good bit. (Look at the video. You have fifty forehands to examine!!)
So you, like Fed, have turned back, two hands on the racquet (left hand high, right hand low), racquet quite vertical, feet in semi-open stance and...
...and you let go with the off-arm hand, which begins to swing toward the net. You don't rotate your torso yet. Your hitting hand moves a bit farther back toward but a bit out from your side. (To try it out just actually copy Fed motions while you watch the slo mo. None of his motions are excess or otional.) The moment of launch arrives.
Simultaneously you do a bunch of things (but I'm only going over them to point out how naturally you'll end up with rotation of the racquet back and lower, call it a flip if you want). Your off arm starts to swing more vigorously leftward,your hitting hand takes the grip lower (how far depends on the spin you want to hit), and then...
...you simultaneously pull your off-arm elbow inward (to shorten the lever arm forcing momentum into your torso), extend your lets up (to force your torso to rotate around to realign with your hips, (which physiology dictates your torso will do), and (still simultaneously, laugh) JUST as your torso starts rotatating because of the leg launch and off-arm pull-in and hip/core muscle flexion.....just then
...you feel your torso is forcing your shoulder and therefore upper hitting arm to start around. So you relax your shoulder, allow (or dammit force) your upper hitting arm to rotate clockwise in the shoulder joint. This rotation will allow your racquet to go back while your torso is rotating forward. Inertia and a very relaxed shoulder/arm will let the racquet lag behind for an instant. It might even look to you like it flipped back, although it is really everything else rotating forward. laugh. So your rotating forward, your racquet is in lag because your upper arm is still in that rotated back position (yes, yes, ESR). Since the racquet head is lagging back you're stuck with the butt cap leading the way forward in a natural sort of assumed leadership. The tension, the power, the motive force...is still the rotating UB, to which the shoulder and arm are permanently attached. So about half way to facing the net your shoulder/upper arm (already having lots of momentum from the UB pulling it along) becomes able to add to the rotation speed by itself flexing, adding some forward swing and some rise of the forearm and racquet.
...at that instant you look like all the other players in the videos. Your off-arm forearm is vaguely pointing forward, your racquet is pointing backward, you're 50% through rotating forward. (If you don't know this natural alignment you just need to look for some good video that captures the player mid-forehand from above. hint:Yandell.)
At that moment you lift the off-arm forehand while (for arm health) rolling the forearm counterclockwise. Simultaneously you intentionally extend the hitting hand forward out toward contact even as the hand/arm has to start going a bit leftward. And (more simultaneous) as your racquet head rises toward the ball powered by everything you've done, you.......unwind that hitting arm that you rolled back clockwise at the start...by using shoulder muscles to forcefully roll the upper arm in the shoulder socket so that you get ISR, yes I said it ISR, call it "partly pronation" (PP) if you wish, up into contact. That rolling into ISR causes further extension out into the ball, causes racquet head rise (uh, spin production), and the extension-plus-ISR may be stared at and called WW) (If you max extension but little ISR you'll hit flat, little WW. If you max ISR and happened to take contact sufficiently in front, you get major WW appearance but stunted extension. Etc.
So in brief, laugh, if you take it back like Fed and initiate like him, there is no flipping to do. The rolling of the upper arm back as the torso starts forward naturally keeps the wrist back (as it was during unit turn), takes the racquet head down, and then looseness leaves that arrangement in place as you max rotation forward. About the grips making a difference: If you hold semi-western or even western...nothing is dfferent than with eastern, except that the racquet is already a bit back and down sooner. If you take eastern, copy Fed precisely, then you still don't have to think about your wrist. Just keep the bend you had taken and held going into the unit turn, and keep the wrist back as your shoulder goes into ESR....and everything will be good.
Or you could just really carefully in slow motion copy every twist and turn Fed makes in the slo mo you are watching repeatedly, with the same synchronization of parts, and you wouldn't have to read much. It sounds so simple, and it is. Well, my hats off to Bender. My fingers are tired.
Edit: Another good example of the off-arm forearm lift into the moment of the hit is Sampras. He majors in the lift. Find a slo mo on youtube and check it out. Problem: I have hundreds of slow motion clips of major players on my laptop...but I can't distribute them. In fact I don't think I know how to post them with this writing. Hmmmm.
