Maybe it's on the coaches. But still, a kid has to deal with the hand he's dealt. Maybe the coach is not (allowed to be) involved with off-season stuff. Maybe he knows that some kids don't like each other, but what's he supposed to do? The point is, a kid in this situation has to deal with it. He can put his head down and do his own work, try to set an example. He can rally like-minded kids to work productively. He can go talk to a coach. He can try to convince the problem kids to pipe down.
Maybe he will later think he dealt with it the wrong way - that's what I mean about learning.