Did you guys ever consider the possibility that the op has poor mechanics? We are talking about simulating a game that professional athletes play (whether Tennis, Golf, or Baseball) who have years of experience.
If a high school kid who doesn't know how to play golf tries to audition for the school team and hits himself in the head with the club, which causes a concussion, you don't sue the school.
Maybe the op should take tennis lessons to learn the proper way to swing a tennis racket or golf club before attempting such a dangerous game...lol.
This is insane.