First and foremost, the kid does have an attitude problem. Secondly, there was no need by the police officer to step forward. Both parties are wrong in this case. Just because you are a police officer with a background being a marine does not give you the right to be Mr. Badass cop. The kid should learn how to play chess and learn how to get a point across effectively, cleverly and most of all without an attitude. All in all, it's cops like this, who have an attitude issue that cause the issues where us the public do not like cops.
On a side note, your parents can go to jail for beating their child. SO WHAT GIVES THE COP THE RIGHT TO LAY A FINGER ON THIS KID?! If the kid stepped forward, I can see that because he was just jumped in his own place, got loads of adrenaline going through him, annoyed pissed off and everything. So let's understand it from his perspective. Add to the fact it took the cops 45 minutes to respond. You have an easily tweaked citizen. Let's mix in a cop with an attitude problem, because he is a cop while being a marine before that. The situation is asking for trouble.
All in all, I see more fault on the cop side than the kids, regardless of him needing an attitude adjustment no matter what the situation. His training in the U.S. military should have taught him that.