This is a defensive drill. It is challenging for the defender because he has to adjust his position with the ball moving. The coach/player with the ball makes different movements on the court so the defender has to react correctly to it. As soon as the offensive player recevies the ball it is a one on one game. The defender has to close out and play defense.

teach the correct defensive position off the ball, close out on the ball, 1-1 defense

The Player after receiving the ball may pass the ball back to the coach and the defender must again adjust the correct position.