Not knowing jack about what happened prior to the little sucker punch the cop gave the perp, I'd say suspend the cop and fine him or give him a "demerit of sorts" and work a sweet yet cheap deal with the perp unless he did something truly bad and move on.
If it weren't a black kid getting smacked by a white cop (with a black cop holding him)who'd care? A couple of years ago some black UC cops in Baltimore I think chased down a purse snatcher on tape and whipped him pretty good. That died down quickly...very little of the Al and Jesse Show. The highest number of black perps killed proportionately in the country and nearly always by black cops is in DC. Where's the outrage? Are all you bleeding hearts upset over a little in your face violence or the race factor or just because you don't like heavyhanded cops? I don't like heavyhanded cops much either but I don't lose much sleep over it.
Fed JBT gungrabbers...that's another matter entirely. I can't stand them.