Service shall begin with the ball resting on the open palm of the server’s stationary free hand. The server shall then project the ball near vertically upwards without imparting spin, so that it rises at least 16cm after leaving the palm of the free hand and then falls without touching anything before being struck.
As the ball is falling, the server shall strike it so that it touches first his court and then, after passing over or around the net assembly, touches the receiver’s court; in doubles, the ball shall touch successively the right half court of the server and receiver. From the time at which the ball leaves the server’s hand until it is struck it shall be above the level of the playing surface and behind the server’s end line.
When the ball is struck no part of the body or clothing of the server, or his doubles partner, shall be within or above the triangular area formed by the net and imaginary lines between the ball and tops of the net posts at a height where it could hide the ball from the receiver. It is the responsibility of the player to serve so that the umpire or assistant umpire can see that he complies with the requirements for a good service.
If the umpire is doubtful of the legality of a service but neither he nor the assistant umpire is sure that it is illegal he may, on the first occasion in a match, warn the server without awarding a point.
If subsequently in a match a service by that player or his doubles partner is of dubious legality, for the same or any other reason, the receiver shall score a point.
Whenever there is a clear failure to comply with the requirements for a good service, no warning shall be given and the receiver shall score a point. Exceptionally the umpire shall relax the requirements for a good service where he is satisfied that compliance is prevented by physical disability.