From what I see on the video, the first 1.5 minutes, he was not resisting. He has so much drugs in his system, his movements were that of someone just trying to stand. The only resistance I saw was the last 1.5 minutes when he refused to go in the car. But, as others have said, even at that, the cops were wrong since they already had him in cuffs and he was hardly a threat.
Here is a possibility that I don't think many of you have considered. The autopsy report says he had bruises and contusions on his head. The cops did not beat or hit him in the head.
It is my understanding that he was thrashing around in the back of the police car, so they dragged him out through the passenger side and held him down.
Could their intentions have been to hold him down so as not to further injure himself from his thrashing?