Occasionally, a player will make a stroke and not know where the ball came to rest. The third Rule in the Rules Email Series covers when a player can play a provisional ball.
When Provisional Ball Is Allowed (Rule 18.3a)
If a ball might be lost outside a penalty area or be out of bounds, to save time the player may play another ball provisionally under penalty of stroke and distance. But, if the player is aware that the only possible place the original ball could be lost is in a penalty area, a provisional ball is not allowed and a ball played from where the previous stroke was made becomes the ball in play under penalty of stroke and distance.
Note that a player is only permitted to play a provisional when the ball might be out of bounds or lost outside a penalty area. If you know that your ball is in a penalty area, you cannot play a provisional.
When a player decides to play a provisional ball, they must announce their intention under Rule 18.3b:
