You have to decide whether you are prepared to take the risk of being attacked for trying to do something about this. Certainly the school, the education authority, the police, the governors should take all the action that is necessary but I can understand your concern if this did not happen on a previous occasion.
You don't say whether you are a parent of a child at the school. If you are, you could talk to any of the governors (the parent governors might be the most suitable ones to approach). It might also be possible to involve local councillors, as they could have some influence with the education authority.