The action key defender is defined as the first defensive lineman INSIDE of the dive key defender. In the diagram shown, the dive key is the first defensive lineman on or outside the play side OT (#1). The pitch key defender is the “next defensive player” outside the dive key (#2). So, the action key in this case would be the 3-tech DT. This is the player that the B-back must read if he indeed gets the ball. He must read how this action key is blocked by his linemen so that he can react and cut off those blocking angles.