Yeah I hope this isn't an idea for a game-able UAV. I wouldn't attend a game with some kind of armed UAV was at that I couldn't fire back at.
If you're a multi-rotor enthusiast and you have the weight capacity, then you could design a type of shield with impact sensors on it. That way you could detect hits and allow people to shoot back at it.
I've also seen protective "cages" that surround the rotors on multi-rotor RC's to protect the blades. These would also protect players from getting cut.