Answer:
Indirect action is your best plan. Just involve school admin and/or police. I'd personally go to school admin first, and if nothing changes before your next class, skip. Contact the professor and explain thoroughly both the situation and your reasoning, hopefully they will understand and help with your missed work/lecture. Use police as a last resort, if you get no reasonable solution from the school. Most schools have rules against threats and acts of violence. If nothing else, walk into class with a video camera (cell phones work great) and stay passive. Walk to and from class with a friend or two to make yourself a less easy target. Do not defend yourself by striking the other student, only control damage to yourself. Hopefully someone will intervene, and at the very least, you will have video evidence of a physical assault on your person, which would be very useful in a court case. This is of course assuming that threat is not an empty one, which I would honestly think it is. Good luck. Try to avoid a physical altercation at all costs, and no matter what do not fight back unless you think your life to be in danger. Unless you're very well trained in self defense that causes little to no injury to the other combatant(Almost none of them are. Most focus on hurting your opponent very badly and very quickly to prevent them from being able to retaliate), you could be brought up on charges of assault yourself, or your case could be weakened. “Violence is the last refuge of the incompetent.
