Above is a link to The Blaze that contains a video of a young female black student, for lack of a better term, flipping out.
The poor instructor, more likely a graduate assistant than a full professor by the look of him, seemed to have no idea of how to deal with the student. She seemed to be set off by a discussion of Darwinism., which caused her to threaten the life of the instructor, various people in class, and ten thousand white people.
The student verbally attacked blacks as well as whites and actually did appear to smack an individual in the head. Eventually one student confronted her and physically removed her from the room.
I taught college for ten years. Thankfully, I never had to deal with anything like that. If I did, I had an advantage in that I am taller and physically stronger, which would enable me to be more assertive.
First, I would have tried to address her verbally. Once a person starts to lose their mind like this woman, you can't reason with her. The instructor should have asserted authority and directed her to leave the classroom after the first offensive diatribe directed at anyone. An instructor, professor, etc is the king in his classroom. He or she must maintain order and enforce respect for himself and other students. Or at least appear to, even when the situation is crazy.
This one stood there looking morose, seeming to try to wish it to go away. That is no way to defuse crazy.
Also, at this point keep a close eye on her hands. If they are going into a large pocket, bag, or backpack, grab hold of the person immediately. No one will blame you for restraining a person in this situation, after what happened at Pitt and Virginia Tech.
You also cannot rule out drugs as a reason for the outburst. Keep in mind that PCP and other drugs reduce awareness of pain and heighten energy levels.
If the crazy person is not armed and is continuing to act crazy, instruct other students to move away from him or her for their own safety. Try to keep the altercation verbal until the police arrive.
But if she starts to get physical, if you have the strength or training, it is incumbent upon you to restrain the student. You are the representative of the school, so it is your job. You don't like it? Tough.
Of course in such a situation, it would be nice to have an All American offensive tackle in the class.
The point is that as the instructor, you have to take charge of the situation and try to protect the other students from harm as much as humanly possible. Being a spectator is not an option.