How a back three covers the backfield as the ball moves across the pitch. When the ball is on one side, that wing comes up into the defensive line while the full-back and the far wing drop deep; as the ball swings across, the triangle swings with it. The rule is two players back at all times. Here the attack kicks into the space behind, and the deep player is already there. The front-line defence is left out so the back three’s movement is easy to follow.