I think the context matters. But once they have the guy under control, which they appear to, then they must stop whacking him. And deliberately smashing his head on the ground is a definite no for me.
As bad as people can sometimes be, everyone wants a police force that shows restraint in these situations. I know there are grey areas and it is easy to be a pompous wiseacre. But sometimes, police officers are not suited for the job because they lose control.