Q. A player plays a ball from a hazard (water hazard or bunker) onto the putting green. Once on the putting green the player realizes the ball he played was a wrong ball. What is the ruling?
A. In match play the penalty for playing a wrong ball is loss of hole (Rule 15-3a).
In stroke play, the player incurs a penalty of two strokes (Rule 15-3b). The stroke played with the wrong ball does not count in his score for the hole. The player must correct the error by playing out the hole with the correct ball (his original ball). If the player is unable to find his original ball he must proceed under the lost ball Rule (Rule 27-1).