Federer's eye-on-ball posture on impact
Gotta say that a while ago, I got my first realization about the essence of "eye-on-ball-during-impact" posture.
I applied my aim somewhat similar to watching the throw of "a dart after you release it" (competitive dart game) or watching the throw/direction of the ball in billiards (competitive pool game). And in golf, watching the launch of the ball in straight line parallel to the ground for a powerful Tiger Woods drive.
I dunno how to explain to in vivid details but I was getting lots of appreciation where all my returns were pretty much solid and has a lot of pace (well, coz i was playing flat strokes). I still have to figure out how to apply advanced stroke like topspin and be able to watch the "throw".
Overall, my observers didn't see any difference at all, and just basing it like a I was having a good day today.