It will be interesting what comes out during the trial. I maintain there is a backstory yet to come out.
They knew each other. Either the cop was giving special punishment to Floyd to teach him a lesson, or, the cop was telegraphing a lesson to someone else via Floyd, but which included Floyd.
The fact that the other cops did virtually nothing, seems to indicate that they knew better than to cross the cop, or do anything other than gently try to convince him to get off his neck.
Think Serpico, and it all makes sense.