i think it is not hitting the ball on the sweetspot. either completely missing the ball or frameshots. all these miss hits can be prevented from simply watching the ball better. for me, i watch the ball throughout the whole point and watch it spin after it bounces towards me. the 2nd reason is probably controlling the height of the ball. once your more aware of how high u want to hit the ball, u will hit less in the net or deep. 3 reason (probably 1 or 2 for some people) is not moving your feet. just being lazy, and not getting any shots in your strike zone what are your thoughts?