I've yelled at a few kids for practicing too hard.
Mostly it involved something that carried a disproportionate injury risk. We're talking about guys that would facemask another, guys that would go for the knees, guys that would hit after the whistle, guys that would hit from behind, and so on. Now if the issue here is normal high-intensity scout team play, that's quite a different story.
My personal favorite involved a guy that was a complete flake and, frankly, a complete idiot. If he was on scout team, he'd mostly stand there and not do anything. As soon as we'd want to see a replay of the previous play (just re-setting and walking through), he'd suddenly because an All-American. Everyone else is doing a half-walk to show who they were blocking, and he's sprinting around and clobbering someone. Needless to say, there were a few run-ins with Mommy and Daddy too.