So, we're saying the mob outside the school are the violent people here and are the ones threatening violence against the teacher. Your logic says that the teacher is responsible, and therefore at fault, if/when they get attacked. The violent people are excused because someone made them attack the victim? Love a bit of victim blaming. Here's a thought - people shouldn't resort to violence, and if they do then they are very much in the wrong. It is not the victims fault that a bunch of violent thugs attacked them.
I once asked a neighbour to stop leaving their waste all over the street as it blew away and caused a mess. I reminded them where bulk uplift should be. They got very aggressive and threatened to give me a kicking. Under your logic, that's my own fault?