Actually if you have a history of martial arts, and I mean like you are a real trained karate expert (get into competitions, win awards, etc.) and if you get in a fight and injure someone, you DO get charged with assault with a deadly weapon. Example is when Mike Tyson got into a car accident, he kicked the person in the balls but didn't knock him out. Why? Because he would have been hit with assault with a deadly weapon.
Anyways I did first think this story was bs. Like damir said, you can't just beat someone up for vandalism and get away for it. It's assault and the cop will arrest him also, if even that's a worse offense. If you see a big ass dude beating up a kid for doing something stupid (such as vandalism), do you think the cop is going to arrest the kid and let the big guy go??? Also I have a hard time believing that you went over the track fine just b/c you shifted the weight foward while the other guy got totaled. I think that if you have more weight in the front, it's harder to go in the air b/c there's more force pushing you down.
And it's hard to get a permit to carry guns in public, especially for younger kids like yourself. It depends what state you are from but most states won't allow you to just lay a gun on a table in public.