Ball in play ( Definitions )
A ball is “in play” as soon as the player has made a stroke on the teeing ground. It remains in play until it is holed, except when it is lost, out of bounds or lifted, or another ball has been substituted, whether or not the substitution is permitted; a ball so substituted becomes the ball in play.
If a ball is played from outside the teeing ground when the player is starting play of a hole, or when attempting to correct this mistake, the ball is not in play and Rule 11-4 or 11-5 applies. Otherwise, ball in play includes a ball played from outside the teeing ground when the player elects or is required to play his next stroke from the teeing ground.
Exception in match play: Ball in play includes a ball played by the player from outside the teeing ground when starting play of a hole if the opponent does not require the stroke to be cancelled in accordance with Rule11-4a.
Palla in gioco ( Sezione II – Definizioni)