Hitting up vs. Brushing up on the serve

[toly]

Originally Posted by sureshs

True. That could also explain the topspin without the racket moving up. But it depends on how long the ball has been sliding down the strings due to gravity. It again comes down to the dwell time near the apex.

IMO the major factor is ball vertical speed. The higher toss the more topspin we can get. Importance of dwell time is not so obvious, at least to me.