Noooooooooo!
*Runs away*
Just to chip in on the Rugby vs. American Football debate:
I'm sure certain athletic types on the American Football team would do pretty well at Rugby, however, I'd dispute
Duke's point about them being surprised by a 300lb Linebacker.
Yes, if they got hit by someone like that at full tilt, it'd be shocking, however a 300lb linebacker is on the gridiron very briefly to do one thing: Spend 10 - 20s at a time trying to stop an opposition player from running by. He's not supposed to come out with the Football / Throwball* and if by chance he does, you very, very rarely see them collect the ball and sprint 90 yards with it to score a touchdown, and then get straight back into the starting lineup and be expected to do it all again. He works in 10 - 20s explosive energy bursts and goes to sit down afterwards, and consequently is generally (but not necessarily always) less physically fit, less agile and flabbier than a Rugby player.
The Rugby player is expected to run, tackle, pass and carry the ball repeatedly for 40 minutes without much of a break (except for Scrums) and then do the same again after halftime (or until he's one of the 7 lucky few who're subbed off or, less luckily, goes off injured!)
*
Delete as regionally applicable