Watch the video again, when that instructor swings his back foot is rolling, and would lift up after he hit the ball if he had a ball in frount of him. Then watch your rear foot it does not roll at all, it starts to lift before you hit the ball. Even on a full swing your rear foot should be rolling down the line when you hit the ball and should do most of the lifting aftre you hit the ball. That will keep you from rotating to soon.