Tennis players are doing it wrong. All of them. Roger Federer? Improper form. Serena Williams? Same. Rafael Nadal, Novak Djokovic? Bad, bad. At least that’s what Professor Tennis believes.

Don R. Mueller, a former physics professor who calls himself Professor Tennis, has been on a yearslong campaign to persuade tennis players that they could be so much better if they considered physics.

He is an advocate for two-racket tennis — meaning, play with a racket in each hand. “Eliminates the problem if you have no backhand,” he said. He also wants players to reconsider how they grip the racket. With a slight adjustment, they could blast their serves so much harder.