Moving screens are becoming as hard to call as block/charge. With all the screen /roll and dribble hand-off action, there are a ton of screens out in the open in today's game. The screener is almost never completely set and usually leans or throws a hip to slow the defender down if they try to come over the top. You could argue that 80% of the screens are illegal and should be whistled. Or you can say that it's part of the game and never call it. The problem is when they don't call it for 35 minutes and then randomly call one on a play which looks like so many others that were no calls.
My biggest complaint with officials is inconsistency within a game. If it's a foul 30 seconds in, it's a foul with 0.1 seconds left. Ditto with traveling, palming, three seconds and all the other calls they make once a decade. Either call it or don't. Just don't make the kids figure out what you're doing. They pick up on what's being called early and adjust. If refs are consistent, it all works. If they aren't it's chaos and a bad game