There's no "quarterback". No "kicker". You can't change the whole team for the defence.
My high school football team (that's American football this time
) is so small, that we can't change out our teams for offence and defence, except maybe a couple of players. I will say that it is very intense, because not only are you actually encouraged to make physical contact with other players, but you HAVE to; otherwise you'll get your ass kicked in. That's why I like it better than soccer. From what I understand, you're not exactly supposed to run the other team into the ground in soccer. Plus, even though the plays are predetermined, it requires a lot of teamwork. If the offensive lineman doesn't block his man, the runningback is pretty much screwed. I would know, I play runningback on my school team.