"Anyone who wears brass knuckles is looking for trouble. If they want protection, they should carry, though I'm not sure what the OK laws are."
I don't know either, but I think you're right. I don't know about OK, but brass knuckles are illegal in most states.
I'm not saying this is not worth pursuing, but the local cops and DA held the guy and investigated and came to the conclusion that it was self-defense. Perhaps it was.
The http://www.packing.org/ shows that OK is a shall-issue state, and recognizes any valid CCW issued by any other state.