Once again, you're making a fucking retarded generalization across a sport with high specialization. While NFL lineman have considerable weight on your average rugby player, NFL cornerbacks probably give up a few pounds to your average rugby player. You are yet again trying to compare apples to oranges. No one is saying an NFL lineman could be competitive in professional rugby, just as we know that a rugby player couldn't possibly compete with an NFL lineman. You're an idiot if you aren't getting this distinction.

And no, it can't be proven by any "fact." First of all, show me the evidence that football players are more likely to be convicted of serious crime independent of socioeconomic status, nationality, race, or gender. Then normalize those factors for rugby and football players. Now you have meaningful data. I mean Jesus Christ, America has more serious crime than Britain. If you take a look at any cross-section of American society and compare it, you'll find they commit more crimes because America has more crime, period. Correlation doesn't imply causation.