If they're off duty and in plain clothes shouldn't it be a civilian assault? Although, since the intent is to paint a federal agent I suppose you'd have a case.
When you go to a paintball field, is there a complicated registration process, or is it just understood that paintball is played at this particular place? Whatever legal maneuvers the paintball field's management has to do, DefCon could do.
(I suspect the main objections to indoor paintball will come from the venue. Perhaps a less messy, but still humiliating, method can be used?)
This is an absurd proposal, but given that the Rio won't let people running pubs in this years call for parties attach stuff to the walls (Can't find the link offhand, but it was in the submission info), I think it's safe to assume that paint guns inside wouldn't happen.
That said, that's the least important reason, the more important one being that you can't just nail people with any kind of gun at an infosec conference, no matter how unconf it is.
