As a wise man once said: "You made my girl cry, now you die."
In all seriousness though, Fujishiro overreacted and we all know it. He said some bad stuff, but it was pretty superficial and falls in line with his job of disciplinary (read totalitarian) control. Don't counter verbal transgressions with physical violence, no matter how angry you are.
On the other hand I am very happy that Fujishiro gets mad on her behalf all the time. Her inner turmoil is overshadowed by how much she likes Kurokawa. This could so easily devolve into her rejecting Kurokawa just because she is jealous, but instead she appreciates her more.
This is pretty much my take on the whole thing. I mean, actually hitting the teacher was like one of the worst ways to go about it but I did like how it showed how much she cares about and wants to protect Fujishiro.
One if the things I’ve always thought odd about society was the idea that physical violence is never ok, but verbal “violence” is. In this example the teachers words could potentially create an emotional scar that could take years to heal, while his bruise will heal in a week. Not to mention how high Japan’s suicide rate is. A large chunk of the cause is probably due to bullying. The main issue with bullying isn’t the physical pain, but rather the emotional and mental pain.
You also have to think about how to resolve an issue without violence, you need the wit and influence to do so, and if you don’t then all that’s left is violence.