<P> A legal serve is any serve which does not fault . A fault occurs if the ball is touched by anything other than the racket, between the time the server throws the ball into the air to serve it and the time at which it lands in the designated service box; service faults are also incurred for missing the ball, stepping across the baseline before striking the ball (foot fault), and walking or running while serving . Two consecutive faults (double fault) result in the opponent winning the point . The receiver must allow the serve to bounce once before returning it, or they lose the point . </P> <P> If the ball touches the net on an otherwise legal serve (this is called a let or net service) the serve is retaken, without being counted as a fault . (On any other return during the point, the ball may touch the net without any consequence .) </P> <P> If a legal serve is made, the players then alternate returning the ball from their side of the court to the opponent's . The point is lost by whichever player first: </P> <Ul> <Li> allows the ball to bounce on the player's own side of the court, and then fails to hit the ball before it bounces again, or </Li> <Li> hits the ball, unless either <Ul> <Li> the ball subsequently bounces on the first bounce in the opponent's court (although the ball may hit the net or another object before bouncing), or </Li> <Li> the ball is subsequently hit by the opponent, or hits the opponent, before it bounces </Li> </Ul> </Li> <Li> intentionally contacts the ball with the racket more than once, without it being hit by the opponent, or </Li> <Li> touches the ball with anything other than the racket (or with the racket if it has left the player's hand), or </Li> <Li> hits the ball before it has passed over the net to the player's side, or </Li> <Li> touches any part of the net with their person, or </Li> <Li> (in doubles) hits the ball after their partner has already done so, before the ball has returned to the other side . </Li> </Ul>

When do you replay a point in tennis