Some times the defense when guarding the ball on a ball screen will try to cheat the play, and jump out over the screen before you actually use it. This is when the ball screen refusal comes into play, and you can make them pay for trying to jump over the ball screen early. Being able to use this move and read the defense comes down to having good basketball fundamentals. If you don't have the correct move to use when the defense makes a certain move, then you are going to be in trouble.
You must keep the defender honest and make him pay for cheating the play, or they will continue to do it all game and the ball screen will not be very effective. This ball screen refusal drill will help teach you the correct way to refuse the screen and then also how to score off of it.