The other week I noticed an article about recent studies of kids and activities, and they showed it wasn't actually true. Kids are getting the same amount of exercise and play as before. (I remember this b/c I put the blame on the pretend sugars that spike blood sugar that are in SO many snack and "kid" foods, and I loved that this article went hand in hand with it)
I'm thinking that the people who think this is OK don't remember how much those big red rubber balls HURT when you get hit by them! I remember!!!
But my elementary school had a HUGE playground area, and the blacktop was the ONLY place balls could be used. The geodesic dome was down the hill (dirt!) and in its own tanbark (beauty bark to some) area with slide, swings, and rocket climby thing. No balls allowed. Then there was the field, only balls during supervised activities. Then there was the other area where me and my friends would play "fort" and house and all sorts of things. AGain, no balls allowed. Obviously, though my school was tiny, our playground was huge, and they didn't want to lose balls or take 10 extra minutes to go have to get the balls that might have been left.
So honestly, I'm with the OP. Sounds like a bunch of kids getting too wild; I'd want them to tone it down a bit. Of course...if they are all eating Uncrustables and given fruit snacks (other than organic ones), it's probably the HFCS causing the way-too-hyper activity and violence of throwing balls too hard.