Amaya is training to move backward on a high ball. She works to keep her body in front of the ball and her chest down. Her footwork is similar to a cornerback in football. Keep your torso forward, hips back, and feet underneath her body frame as her feet shuffle backward. This helps hold a solid platform and presses the ball forward. Watch and listen to Amaya speak at the end of the drill.
Here is a link to learn more. https://www.stack.com/a/develop-drop-and-drive-defensive-movements-for-volleyball