Q. The shaft of a player's club breaks during his downswing. The player stops his swing short of the ball, but the clubhead falls and moves the ball. What is the ruling?
A. The player did not make a stroke - see Definition of "Stroke."
If the ball was not in play, i.e. the incident involved a tee shot, no penalty is incurred, and a ball must be played from the teeing ground.
If the ball was in play, the player would incur a one-stroke penalty under Rule 18-2a or -2b and the ball must be replaced.