Foul or incidental contact?

[BillyMac]

Originally Posted by Coach Bill

I've heard several officials blow the whistle, shout illegal, and point the other way on this call. What are they referring to if not an illegal screen?

There is no signal for an illegal screen. The most often used signal is a stop the clock fist, followed by a blocking foul signal (hands (not supposed to use fists) on hips), followed by a team control foul signal (punch), sometimes (not required) followed by some verbiage about an illegal screen.

The blocking foul is called due to illegal contact (block) as described as illegal activity in the principles of screening.