Volleyball Drill Demonstration
2 players stand on either side of the net, and the receiver starts with the ball by overhand passing it across the net. This player then passes to their team mate who overhand passes it back for the spike. The receivers are ready to dig the ball back across the court. Have receivers changing positions after every 4 attempts.
Digging and changing position requires players to be able to move quickly when in a low position, enabling them to be more efficient when digging. Being in a low position also helps players assess the ball's trajectory.
When coaching pro players, you may ask the receivers to have their back turned to the net and on the coach's call they turn and dig the ball back, requiring them to react quickly.