If you could make your own field...

This has slight bounds to reality, but as long as its slightly possible anything goes.

When I was little I wanted to play paintball. I thought of this one idea that uses a go-kart

Add metal all the way around a three-seater go kart (probably have to be custom built the third seat would be in the back), but in plastic/tough glass windshield. Add doors. Cut a slot in the metal in front of the passener seat and mount a paintball marker. For the third seat cut a whole out of roof and add a thing that spins, the turret could move, add armor, add freakin huge paintball gun (possibly machine gun)

then I got another idea... what if you got helicopters?

get a plane that classified as ultralight so you dont need a licsnce and use it as air support

MT. Vigilante wrote: An urban environment whould be great, and I mean the real deal, like a small town with finished buildings completely furnished. With many multi leveld buildings and cars parked alongside the road. And the whole town whould be surrounded by some woods, wich are full of bunkers. In the center of the town whould be the town hall with a steeple (like you see many small town halls) at the top of which is the flag that must be captured. Yes I give this subject alot of thought.

I just found this place last night and am already planning my trip.  I think Bedlam is what you're looking for.