How far can a teacher go when it comes to behavior issues with a student who is violent against them?

I think I am understanding your question and that you are asking what a teacher can do if a student gets too violent. If so ... They can press criminal charges against the student. Teachers that have severe discipline issues document what takes place with their students. This is done again each time the student leaves and visits the principals. In certain cases, the school automatically calls the police, the school board is notified, parents are called, and actions can be taken to have a student suspended, expelled, or transferred to another school, a behavioral school, or at least from that class. In many cases, the school seeks legal assistance when they see issues. Often, before the teacher does so on her own.