Unless a fault or a let is called, the ball is in play from the moment the
server hits the ball, and remains in play until the point is decided.
USTA Comment 11.1: Is a point decided when a good shot has
clearly passed a player, or when an apparently bad shot passes over
the baseline or sideline? No. A ball is in play until it bounces twice or
lands outside the court, hits a permanent fixture, or hits a player. A ball
that becomes imbedded in the net is out of play.
USTA Comment 11.2: Must an out call on a player's shot to the
opponent's court be made before the opponent's return has either
gone out of play or been hit by the first player? Yes.