Cancer is uncontrolled cell growth/replication...... so any time cells grow/repair it can happen........... so that's normal body growth, skin cell shedding, blood cell formation etc... etc.... etc..... you are more at risk from playing in the sun than from paintball hits as UV can trigger a cancerous growth. Or from smoking in the safe area, or eating barbecued food in the safe area (polycylic hydrocarbons....... just like those in smoke from incinerators) if you avoided everything that was a potential carcinogen, then all you'd be able to consume is meltwater from arctic permafrost. Otherwise, everything is a potential risk.............. but if you add up all of the ones that are out there and avoid them, you'd still not reduce the risk of cancer as much as by stopping smoking/standing near smokers.
Having said that, a shot in the pills really hurts, and can cause major damage if a clot forms and doesn't clear, the same stands for any tissue. Problem with the nuts is that they are very exposed and not well protected.......... they can't be as they'd overheat and cook your little soldiers. So basically you're getting hit in something that's as susceptible as an internal organ..... just like the eyes, they aren't well protected as they wouldn't work with a layer of protective tissue/fat.
I'll guarantee anyone who takes a good one in the plums starts wearing a box next tourney
Oh, and I take lots of repeated injury at work (special needs teacher) my hands are covered in scar tissue and I'm constantly bruised...... ask anyone who knows me the states I get in. I've looked into this for my own health and it's not considered a big cancer risk. the cells in your body are constantly replaced...... skin an blood most frequently, a few bruises aren't going to increase the chances of a carcinogenic mutation by much.