Yeah I'm curious as to what he did leading to the start of this video.
Why was he taken to the ground in the first place?
It looks like he was resisting arrest, which as history has proven can be extremely dangerous. You can see this by observing the cops having to apply force to pin hims arms down. Now with that said, this type of force should only be used to restrain someone who is resisting arrest (assuming you have exhausted all other [easier] means of doing so). Now I'm not defending the cops but from the looks of this video they were unable to subdue the man so as to place him in handcuffs. Clearly they didn't need to punch him in the face, but the question remains:
If you are trying to restrain a suspect who you believe to be dangerous, and this suspect is not letting you arrest him, what are you supposed to do?
Also: What would have been the outcome if the guy willingly did what the cops told him to and let them place him under arrest?
As I have seen over the years it is usually the suspect who engages into this type of situation, upon which the cops take it to a much greater and sometimes lethal level of action.
I'm not defending anyone in this video, I'm just going off what I saw. This video clearly shows the cops using excessive force, but that is all it shows.
PS: This IS NOT normal cop behavior.