As a mom of a D3 paintball player - I would make a sheet cake like a field with bunkers spaced out. (scroll down to look at the New Jersey layout)
You could do the PSP logo (the red and white) or if they kid has a professional team he follows - decorate one in the team jersey.
Also - you can put actual paintballs on the cake. They are 100% non toxic and edible (they taste horrible)