Video Breakdown and Analysis (Video)

[JetMetFan]

But, and I agree with deecee on this, you may not know whether it "matters" at the moment it took place.

Take the play in the OP. Some have said illegal, some have said play on. Off of the screening activity B#21 ends up in an advantageous position: He's in the middle of the lane with inside position on the closest defender. The thrower didn't give him the ball because there was another defender in the way. Now, suppose the defender guarding the thrower was shading towards his - the defender's - left instead of the right? B#21 probably gets the ball and has a good scoring chance. It's going to be tough to put a whistle on an illegal screen at that point.

We can also look at the play the way it took place, but with a twist. B#21 winds up in an advantageous position but the ball goes to B#3 outside the 3-point arc. If B#3 catches the pass cleanly there's a chance he attempts a 3-point shot. If he shoots, B#21 has inside position for rebounding. Again, we can't always immediately know the ramifications of potentially illegal contact especially when it's off-ball contact.