The legal table tennis serve

The open palm prevents the server from spinning the ball with the fingers before the toss. "Stationary free hand" prevents a moving hand from disguising the release. "Without imparting spin" closes the same gap again. And the 16 cm minimum rise ensures the ball is genuinely tossed rather than flicked straight into the bat.

Read together, they are not arbitrary technicalities — each one removes a specific way of hiding information from the receiver.

From the start of service until it is struck, the ball must be above the level of the playing surface and behind the server's end line. And it must not be hidden from the receiver by the server or the server's doubles partner, or by anything they wear or carry.

As soon as the ball has been projected, the server's free arm and hand must be removed from the space between the ball and the net — a space the Laws define precisely as bounded by the ball, the net and the net's indefinite upward extension.

As the ball is falling, the server strikes it so that it touches first their own court and then touches directly the receiver's court. In doubles, the ball must touch successively the right half-court of the server and then the right half-court of the receiver.

Singles has no such diagonal requirement. A singles serve may go anywhere on the opponent's side of the table, which is a common misconception among players who have learned tennis first.

It is the player's responsibility to serve so that the umpire or assistant umpire can be satisfied the service is legal; either may decide that a service is incorrect.

If an official is not sure about the legality of a service, they may — on the first occasion in a match only — interrupt play and warn the server. After that, any subsequent service by that player or their doubles partner which is not clearly legal shall be considered incorrect. The benefit of the doubt is available exactly once.