The suspect may not have resisted arrested before the police got him on the ground, but he may have resisted arrest after they got him on the ground. Just because a suspect is laying on the ground doesn't mean that he's cooperating fully with the police by allowing them to handcuff him. If a suspect doesn't cooperate by either struggling with the police or by having one or both of his hands under his body, the police can use whatever force is necessary to get the suspect to comply and to get him handcuffed. One method that police are allowed to use is to hit a suspect on his shoulder or arm with their flashlight or baton until the suspect complies with the police's instructions.
There were so many cops on him, we couldn't tell if the suspect was resisting. From what we could see, the cops were hitting him all over the place. A good smack upside the head, imo, should have been sufficient to knock the guy out.
After the Rodney King beating, I was asking myself why police don't use tranquilizer dart guns like fish and game does. Situations like these, gives LE a big black eye.