Originally Posted by Chas Tennis
I'm not sure who you are asking. I proposed a question only about the initial ball contact location, first contact, and a simple way to crudely observe it with videos.
thanks for your answer and I agree this is a challenge with most available video. With high speed video on strong top spin shots, there are 2 points of reference (at least) for us. One is the initial contact you suggest and the other is location at full pocket depth. seems the full pocket depth is lower and more indicative of the action you expect.