How?

How can it be that a person(s) can record that cop brutalizing a man? How can that person do nothing but just watch? I couldn't stand to do nothing, regardless if other cops are around. I'd probably run and tackle the asshole.  Then I'd probably be arrested, but so be it.

Hopefully I wouldn't pull my weapon and shoot the cop. I think that would be justified, but "the law" most likely disagrees.