I played today, and my playing partner was just about to tee off. After addressing the ball, and starting his backswing, a gust of wind moved the ball off the tee, it fell off just as my partner was 1/2 way through his downswing. He could not stop his swing, and continued to swing at the ball, which he hit. The thing is, the ball was still moving (after just having fallen off the tee) when he hit it. He actually made good contact and hit it in the fairway.
What is the rule in stroke play? 1 stoke penalty?