I want to do this with my church youth group:

Buy a bunch of nerf guns and bow&arrow and nerf weapons. Have them in the Pavillion like a cornucopia. Each person playing has a sash with 3 colored ribbons on it, thats thier 'lives' a headshot (Only guns with the rubber darts can get a headshot for safety reasons) claims all 3 ribbons. A chest or stomach shot gets 2 ribbons and a anywhere else gets one. Sponsors can be people watching the game who buy lives and weapons and ammo with real money and the collected money goes to the church.