You don't play on until you come off your line, which is where you mark the ball. Ergo, he marks the ball in front of the line, his momentum takes him across the line, he runs back into play, it isnt play on until he has crossed the line at which he marked the ball, which by definition is inside the play. Then he kickd the goal. He can't have played on from behind the goal line because he hasn't yet crossed the line of where he marked the ball. Any suggestion this is an error is just simply incorrect.
