While the guy was being dick to police, there is no justification to such police brutality.
First of all, if they already got him down and he wasn't even moving anymore, why did the policeman hit him twice with the baton for no reason whatsoever.
Policemen in this video are just savages that will do everything to "prove" their superiority, and it's a trend that I've noticed with majority of the policemen in the US from these articles and general public feedback. I think most of them lack training, or simply aren't being punished for improper actions while on duty.
If you look at police in UK, they can't even use physical force against you before they give a warning. If something like that would've happened here, policemen would definitely lose their jobs and possibly get jail time as well. And that's a good example of civilised society where police respects citizens and vice versa.
USA policing system is just flawed to the core, where physical detention is put way above respect and human rights.