Pick N roll or Moving Screen

[Jurassic Referee]

Originally posted by Hawks Coach

So it is screen, hold til contact, pivot immediately on contact to a new position that is advantageous to the offensive player. Pivot after defense stops and before defense reacts and begins to move again, because pivoting into a moving defender and hindering that movement is a foul.

Great description, Coach. That's basically what I look for on pick'n'roll plays:
1) Did the screener get there in time? If not, illegal block.
2) If they got there in time, did they then set a legal screen? If not, it's usually because they are "rolling" early and into the straight line path of a moving defender, and then hipping them or using "butt" contact to slow the defender down. Foul on screener. If the screen is legal, I ignore or no-call the subsequent collision even if the result may be fairly heavy contact and displacement. Similar to what Rut was saying, I think. The screener has gained their team an advantage by completing the successful screen. Calling the contact a foul on the defender now just gives the offensive team a second advantage on the same play that was not really intended under the screening rules.
3) Did the defender see the screen and still try to push through the screen? If so, call the contact on the defender if you feel that he's gaining an advantage by getting through quicker, or the contact is rough or excessive.
4) Finally, just as you said, I look at the screener to see if they "roll" into the defender. If so, and the contact gains them an advantage- illegal block.