The video is disturbing.
I'm not sure it's uncommon. I've seen cops react violently when someone assaults them or resists arrest.
Who knows what preceeded this, or what the guy was doing. We do know he's got criminal baggage and he violently resisting.-- it sure took a lot of well trained men to subdue him.
it's human nature to try and save your life... What some see as "violently resisting" can also be interpreted as someone trying to save/defend their life.
He was unconscious for most of the video.. hard to say he was resisting.