[BillyMac]

13) If a blind screen is set on a stationary defender, the defender must be given one normal step to change direction and attempt to avoid contact. If a screen is set on a moving defender, the defender gets a minimum of one step and a maximum of two steps, depending on the speed and distance of the defender. A moving screen is not in and of itself a foul, contact must occur for a foul to be called.

Thanks to Mark Dexter and rainmaker.