As he approaches the kicker, the last man to beat, he's angling towards the sideline. If he had kept that angle, the kicker may have been able to just push him out of bounds. But the kick returners were coached to run at the defender when they had just one defender to beat. You can see Marion do that in the play. He angles more upfield, and almost directly at their kicker. Then, as he approaches, he breaks outside and not only has the speed but plenty of room to run past the kicker. Great coaching and execution there.