I strongly agree that the kid needs to learn to deal and cope and that that is part of growing up, Like I said, I think the kid should have called the taunter on it right then and there. But I don't agree that the school, coach, etc have no responsibility in setting parameters and enforcing a culture -- though I'm not sure you meant to imply that (wouldn't want to be uncharitable.) A school is an educational institution, not just a free-for-all, where kids are left to fend for themselves, and learn life lessons the "hard-knocks" way. A team is a school activity. It's only justification for existence is not to win games, but that it contributes something to the moral, social, and intellectual development of what are still children -- though on the cusp of becoming adults. Yes, they should be given lots of space in which to work out issues among themselves. But saying that the coach, AD should never be brought in strikes me as a cop-out, let's them abdicate their responsibilities as teachers and educators.
Imagine if the coach knew about such taunting and said, "work this out between yourself; it's part of growing up." I would think most people would find that an absolutely appalling and irresponsible response.
So what's a parent to do when there isn't a culture of accountability in place? Just leave it be? I can see something to be said for that. But that can't be the limits of it.