American Football

　　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.

　　Ground Rules

　　Football is a game of inches played on a field measured in yards-English measurements are used to track movements on the field.Teams succeed based on how many yards they accumulate or allow. An official NFL (National Football League) football field is a rectangle that is 120 yards(110 m) long and 53 yards. I foot (49m) wide. Most fields are covered in grass and set in an outdoor (open-air} stadium. Some fields are made of artificial turf, which you'll find in many of the indoor stadiums.

　　The most essential piece of equipment in a football game is the ball.Official NFL footballs are handmade by Wilson Sporting Goods Co. The football is an oblong (椭圆形的) sphere and has a lengthwise circumference(周线) and a width-wise circumference in the middle of the ball.

　　With the equipment identified and the field set, we can now play a game.An NFL game is divided into four quarters with an extended halftime break between quarters two and three. Each quarter is 15 minutes long. lf the teams are tied after four quarters of play,they play an additional overtime period of 15 minutes. Inthe overtime, the first team to score wins.

　　While the game time adds up to one hour, it usually takes three to four hours to play a game. Teams can stop the clock by running out of bounds,throwing an incomplete pass, or calling a time-out, of which they have three per half. Time also stops for each of the two-minute warnings, observed two minutes prior to the end of the second and fourth quarters.

　　Who's Who

　　An NFL roster allows for no more than 53 players on a team. At any one time, only 11 players per team are allowed on the field. To understand an NFL roster, you have to identify the three teams within a team: theoffense. the defense and special teams. Each of these groups has specialized positions with a specific setof skills.

　　Offense

　　A team's offense is responsible for taking the ball down the field toward its opponent's end zone. To do this. the offense throws the ball from one player to another or holds the ball and runs forward. Here are the basic offensive positions.

　　Quarterback (QB)-This player throws the ball to receivers or hands it off to running backs. The quarterback is also known as the "field general,"because he's the on-the-field leader.

　　Offensive linemen-These players provide blocking for the quarterback and running backs. Individual linemanpositions include:

　　Center (C)-The center is located in the middle of the line. This player hikes the ball to the quarterback by bringing the ball up between his legs.

　　Guards (LG/RG)-These two players flank the center.

　　Tackles (LT/RT)-The tackles are positioned on the outside of each guard;teams have two tackles.

　　Receivers-Receivers run down the field and catch balls thrown by the quarterback. Receivers are either wide receivers (WR) or tight ends (LTE/RTE).depending on where they are positioned on the field.

　　Running backs-Running backs take the ball from the quarterback and run up the field. Depending on the fomation (arrangement of the offensive players, a running back might be called a tailback (TB), halfback (HB) or fullback (FB).

　　Defense

　　When a team does not have possession of the ball, it is on defense and uses various methods to prevent theother team's offense from scoring. These players must tackle the offensive player who has the ball to stopthe offense from advancing.Defense will also try to take the ball away from the offense.

        （实习编辑：王晓晓）