Originally Posted by 5263
but they are very related though
the tennisspeed guy say that the racket already starts slightly closed (by a slight pronation of pat the dog move as the acceleration starts) but he also says players would intentionally hit below center to make the racket twist over the ball.
he thinks that the pre contact closing is important but I think he thinks the main contributer is how low you hit the ball on the stringbed
however I'm not sure if those hits are really wanted or in fact shanks, because as great as fed is he always was prone to shank a few (probably because of his extreme spin generation).