Rules

21. Player Hinders Opponent
If a player commits any act which hinders his opponent in making a stroke, then, if this is deliberate, he shall lose the point or if involuntary, the point shall be replayed.

Case 1. Is a player liable to a penalty if in making a stroke he touches his opponent?
Decision: No, unless the Umpire deems it necessary to take action under Rule 21.

Case 2. When a ball bounds back over the net, the player concerned may reach over the net in order to play the ball. What is the ruling if the player is hindered from doing this by his opponent?
Decision: In accordance with Rule 21, the Umpire may either award the point to the player hindered, or order the point to be replayed (see also Rule 25).

Case 3. Does an involuntary double hit constitute an act which hinders an opponent within Rule 21?
Decision: No.

USTA Comment: "Deliberate" means a player did what he intended to do, although the resulting effect on his opponent might or might not have been what he intended. Example: a player, after his return is in the air, gives advice to his partner in such a loud voice that his opponent is hindered. "Involuntary" means a non-intentional act such as a hat blowing off or a scream resulting from a sudden wasp sting.