Jim Stone describes the collapse dig, where the defender drops forwards to her knees and hips to get the platform underneath the ball.
Defense is a forward game. In preparation for the dig, the defender should stay low, forward on her toes and ready to move forward. In this video, Hentz picks up a hard and fast attack by collapsing onto her knees and dropping the hips to maintain an upright torso. She's able to get her platform underneath the ball because she was already so low in her base defensive position.