美式足球英文介绍3句
American football is a unique sport -- it is a game about gaining territory as much as it is about scoring points. When two teams step onto a football field, each is battling for every inch it can take from the other. Each team wants to defend the field that is behind it and invade the field in front of it. Ultimately, they want to gain enough ground to score a touchdown or field goal.
http://entertainment.howstuffworks.com/football.htm
use soccer，Football is a game played by two teams of eleven players using a round ball. Players kick the ball to each other and try to score goals by kicking the ball into a large net.