Pick and Roll Motion

[TigerBball]

I asked this about a year ago, and got various answers, but the MSU / UK game sparked my interest again.

This comes from a coaching perspective, but I want to teach it correctly, but still confused.

An MSU player set a screen for the ball handler. UK switched. the MSU screener then rolled, keeping defender pinned and backed him down into the lane and posted up creating a little trying to guard a big.

From my understanding of the post last year, this should have been a foul for displacing the defender. I understand not everything gets called, but I just don't see players being called for pinning or posting up players after setting a pick and roll when the defenders switch.

The reason I noticed this was the screen was set at the top of the key and pinning / backing in motion took the defender all the way down to the block.