Rules of Golf No. 14-5: Player Moving Ball
Rule 14: Striking the Ball
5. Playing Moving Ball
A player must not make a stroke at his ball while it is moving.
— Ball falling off tee (Rule 11-3)
— Striking the ball more than once (Rule 14-4)
— Ball moving in water (Rule 14-6)
When the ball begins to move only after the player has begun the stroke or the backward movement of his club for the stroke, he incurs no penalty under this Rule for playing a moving ball, but he is not exempt from any penalty under Rule 18-2 (Ball at rest moved by player).
Penalty for Breach of Rule 14-5:
Match play — Loss of hole; Stroke play — Two strokes.