Here are the basic defensive positions:

　　Defensive linemen-The linemen put pressure on the quarterback by trying to tackle him before he releases the ball. They also try to stop running backs.There are typically three or four defensive linemen.

　　Linebackers-When there are four linemen, there is a middle linebacker(MLB) and two outside linebackers (OLB). When there are three linemen. there are two inside linebackers (ILB) and two outside linebackers. Their job is to back up the linemen. as well as contain runners and cover receivers on some plays.

　　Cornerbacks (CB)-The cornerbacks prevent the wide receivers from catching the ball by breaking up passes from the quarterback.

　　Safeties-The safeties play deep behind the rest of the defense to prevent a long pass or run. A strong safety (SS) lines up on the side of the field where there are more offensive players. The free safety (FS) plays a deep, middle position.

　　Special Teams

　　If a team has to kick the ball, it uses its special-teams unit. This unit includes the team's kickers, theoffensive line, and players who run down the field to tackle a returner(see below).

　　Placekicker-The placekicker kicks the ball through the goalposts to score points and kicks the ball to theother team to start the game and after each scoring possession.

　　Punter-The punter free-kicks the ball if his team cannot advance the ball down the field.

　　Returner-During a kickoff or punt, the returner tries to catch the ball and return it as far as he can. A player can score a touchdown on a rcturn.

　　Moving the Ball and Finding the End Zone

　　A football game begins with a coin toss to decide which team will receive the opening kickoff. From the opening kickoff, the two teams battle to take possession of the ball. Possession means that a team's offensive unit has the ball.

　　A team can take possession of the ball in several ways:

　　Receiving a kickoff-A team receives a kickoff at the beginning of each half and after the other team scores.

　　Turnover-A team recovers a ball dropped by the other team (fumble)or picks off a ball thrown by the other team's quarterback (interception).

　　Safety-A player is tackled in his own end zone, meaning the end zone his team is defending, so the other team gets the ball though a free kick.

　　Punt-The defensive team stops the offensive team from getting 10 yards in three downs, and the offensive team free-kicks, or punts, the ball to the other team on third down.

　　Turnover on downs-The offensive team fails to advance the ball lO yands in four downs and has to surrenderthe ball to the other team.

　　For those new to the sport the last two scenarios on this list may not make sense. One of the most confusing concepts of American-style football is the down-and-distance system. Every time a team takes possessionof the ball, it is given a set of four downs, or attempts, to move the ball l0 yards. If the team can movethe ball lO yards or more Within four downs, the team gets another set of four downs to go another l0 yards, and so on. For instance, if a team advances 3 yards on first down, the next play is second down with 7 yards to go (second and 7); if the team then advances 5 yards on second down, the next play is third and 2; if the team then advances 2 or more yards on third down, the next play is back to first and lO, wich a whole new set of four downs during which to advance the ball.