American football is a sport played by two teams of eleven players on a rectangular field with goalposts at each end. The offense， the team with control of the football （an oval-shaped ball）， attempts to advance in the field by running with or passing the ball， while the team without control of the ball， the defense， aims to stop their advance and take control of the ball for themselves. The offense must advance at least ten yards in four downs， or else they will turn over the football to the other team； if they succeed， they are given a new set of four downs. Points can be scored by advancing the ball into the other team’s end zone for a touchdown， kicking the ball through the opponent’s goalposts for a field goal， or tackling the ball carrier in his own end zone for a safety. The team with the most points at the end of a game wins.
　　美式足球是一種由每队十一个球员组成的两支队伍，在末端各有两支球门柱的矩形场竞技的体育运动。进攻方，控制橄榄球的队伍（一个椭圆形的球），试图在比赛中用运球和传球的方式推进；而没有控球权的队伍，即防守方，旨在阻止他们推进，并抢回控球权。进攻方必须在四次进攻机会中推进至少十码，否则他们将转交控球权给对方；如果他们成功了，他们将获得一套新的四次进攻机会。获得分数的方式有将球推进至对方队伍的端区达阵得分，将球踢过对方两支球门柱的中间射门得分，或者在持球者的端区拦截成功安防得分。在比赛结束时得分最多的队伍获胜。
　　American football is the most popular sport in the United States. Professional football and college football are the most popular forms of the game， with the other major levels being high school and youth football. As of 2012， nearly 1.1 million high school athletes and 70，000 college athletes play the sport in the United States. The National Football League， the most popular American football league， has the highest average attendance of any sports league in the world； its championship game， the Super Bowl， ranks among the most-watched club sporting events in the world， and the league has a revenue of around $10 billion every year.
　　美式足球是美国最流行的体育运动。职业橄榄球和大学橄榄球都是最流行的比赛形式，高中橄榄球和青少年橄榄球则是另一个重要层次。在2012年的时候，美国有近一百一十万名高中运动员和七万名大学生运动员参与这项运动。国家橄榄球联盟，美国最受欢迎的橄榄球联赛，享有世界上所有体育联赛的最高平均出席率；它的总决赛，超级碗，是世界上最受关注的俱乐部体育赛事，并且联盟每年的年收入约为十亿美元。