If the basketball player using the ball screen isn't a very good shooter than there is a good chance that the defender is just going to go under on the ball screen action. However there is a way to make the defense pay for going under, even with a poor shooter.
When the defender goes under the ball screen, the big man can immediately turn around and re-screen them. This time the screen is even lower the not so good shot from the 3 point line becomes a much higher percentage 15 footer if the defender chooses to go under again. Being able to read the defense and make the correct read on the ball screen is important for any player that is going to handle the basketball in a game. This is a great drill to teach you the basketball fundamentals of this type of screen.