When playing in his prime, Tiger Woods was famous for being able to abandon a shot, even when he had started his downswing. He had enough self-control and physical strength to stop the clubhead halfway down when he felt something wasn’t quite right.
That’s permitted within the Rules. In the definitions of the Rules, it says that a stroke has not been made if a player decides to stop during the downswing and is able to do so by deliberately stopping the clubhead before it reaches the ball.
