I know, i might get some heat for making this statement, but will still say it
The police was called to the place by someone claiming, he had no authority to stay there. They get there:A half naked guy sleeping in a youth center (he looks like a drunk or homeless on the video) whatever happens i cant hear, but they want to arrest him, probably figuring out if he is allowed to be there and he is clearly resisting arrest and being quite unruly... In america, when you resist arrest and start fighting with cops you get beaten up, until the cuffs are on and thats what happened here.
Would he have been better of getting tasered?
The cop does give a very bad picture in his boxing position, not defending him 100%, but i do think its not as bad as guys make it.