Here is the example video: https://www.youtube.com/watch?v=ALNIPwh8I54 (a little violent but not too much)
Given the answers to Are you allowed to strike a person if they say you can? and Does anyone know if this counts as assault? it sounds in most situations hitting a person is always illegal (unless they attack you first).
What about this one? If the person threatens violence, can you act preemptivley? Also, technically speaking in the video he never explicitly threatened violence, just acted in such a way that strongly implied it (getting up in people's faces and taking shirt off). Could this be used in his defense?