Originally Posted by Richie-Rich
I know, that being said you aren't going to charge someone without protection like you are with the false sense of invincibility you get in body armor. Even if the armor does offer great protection, nothing is going to protect you against the forces you will encounter by a 350lb man charging you at top speed and hitting your mid back with hard shoulder.
Not to beat this into the ground, but I'm going to..... but a 270 lb. lock sprinting at you knowing that he won't be "rescued" by a whistle being blown every 7-10 seconds stopping play is also a little different--he knows he has to finish the job and not wait for the play to stop. And he'll hit you mid-back, mid-chest, mid-anything, and he'll grab anything he can.
There's also an argument to be made that an offensive lineman in American football is encouraged to get up to 350 lb. because he won't be expected to run and he won't be expected to be flexible enough to survive a scrum or a maul, ruck, etc.
Another difference between the two is the role of coach during the game. Rugby players have to think more on their feet.
American football has much more specialty of position, encouraging players to develop highly in their skill sets, e.g. quarterbacks, running backs, punters, etc., so the passing and kicking is more precise.
Whereas in rugby football, there is the general separation between forwards and backs, but each player has to be more well-rounded, able to kick, start plays, win mauls/rucks, kick, etc., and score.
An interesting way to settle the friendly rivalry between the two sports is to ask players: rugby players are typically more than willing to try American football (look at the growing number of Islanders in the NCAA and NFL); football players don't often want to play rugby (unless they are a special teams player who has been coached in the "rugby style.")
Of course, we can get into the differences between rugby union v. rugby league, too, not unlike American football v. Canadian football.