Scoring

A kicker attempts an extra point.

A team scores points by the following plays:

• A touchdown (TD) is worth 6 points. It is scored when a player runs the ball into or catches a pass in his opponent's end zone. A touchdown is analogous to a try in rugby with the major difference being that a try requires the player to place the ball on the ground.
  • After a touchdown, the scoring team attempts a conversion (which is also analogous to the conversion in rugby). The ball is placed at the other team's 3-yard (2.7 m) line (the 2-yard (1.8 m) line in the NFL). The team can attempt to kick it over the crossbar and through the goal posts in the manner of a field goal for 1 point (an extra point or point-after touchdown (PAT)^[9]), or run or pass it into the end zone in the manner of a touchdown for 2 points (a two-point conversion). In college football, if the defense intercepts or recovers a fumble during a two point conversion attempt and returns it to the opposing end zone, the defensive team is awarded the two points.
• A field goal (FG) is worth 3 points, and it is scored by kicking the ball over the crossbar and through the goal posts (uprights). Field goals may be placekicked (kicked when the ball is held vertically against the ground by a teammate) or drop-kicked (extremely uncommon in the modern game, with only two successes in the last 60 years). A field goal is usually attempted on fourth down instead of a punt when the ball is close to the opponent's goal line, or, when there is little or no time left to otherwise score.
• A safety, worth 2 points, is scored by the defense when a ball-carrier is tackled in his own end zone. Safeties are also awarded if the offense fumbles the ball out-of-bounds in the end zone, has a kick blocked out of the end zone or commits certain penalties in the end zone. Safeties are relatively rare.

Kickoffs and free kicks

Each half begins with a kickoff. Teams also kick off after scoring touchdowns and field goals. The ball is kicked using a kicking tee from the team's own 30-yard (27 m) line in the NFL and college football (as of the 2007 season). The other team's kick returner tries to catch the ball and advance it as far as possible. Where he is stopped is the point where the offense will begin its drive, or series of offensive plays. If the kick returner catches the ball in his own end zone, he can either run with the ball, or elect for a touchback by kneeling in the end zone, in which case the receiving team then starts its offensive drive from its own 20 yard line. A touchback also occurs when the kick goes out-of-bounds in the end zone. A kickoff that goes out-of-bounds anywhere other than the end zone before being touched by the receiving team is considered an illegal procedure penalty, and the ball will be placed where it went out of bounds or 30 yards (27 m) from the kickoff spot, depending on which is more advantageous to the opposite team. Unlike with punts, once a kickoff goes 10 yards, it can be recovered by the kicking team. A team, especially one who is losing, can try to take advantage of this by attempting an onside kick. Punts and turnovers in the end zone can also end in a touchback.

After safeties, the team that gave up the points must free kick the ball to the other team from its own 20 yard line.

Penalties

Fouls (a type of rule violation) are punished with penalties against the offending team. Most penalties result in moving the football towards the offending team's end zone. If the penalty would move the ball more than half the distance towards the offender's end zone, the penalty becomes half the distance to the goal instead of its normal value.

Most penalties result in replaying the down. Some defensive penalties give the offense an automatic first down. Conversely, some offensive penalties result in loss of a down (loss of the right to repeat the down). If a penalty gives the offensive team enough yardage to gain a first down, they get a first down, as usual.

If a foul occurs during a down, an official throws a yellow flag near the spot of the foul. When the down ends, the team that did not commit the foul has the option of accepting the penalty, or declining the penalty and accepting the result of the down.

A few of the most-common fouls include:

• False start: An offensive player illegally moves after lining up for--but prior to--the snap. Since the ball is dead, the down is not allowed to begin.
• Offside: A defensive or offensive player is on the wrong side of the ball when the ball is snapped. This foul occurs simultaneously with the snap.
• Holding: Illegally grasping or pulling an opponent other than the runner.
• Pass interference: Illegally contacting an opponent to prevent him from catching a forward pass.
• Delay of game: Failing to begin a new play after a certain time from the end of the last one.
• Face mask: Grasping the face mask of another player while attempting to block or tackle him.
• Illegal block in the back: A blocker contacting a member of the opposing team (who is not the runner) in the back and above the waist.
• Clipping: A blocker contacting an opponent (who is not the runner) from behind and at or below the waist.

Under certain circumstances clipping and blocking in the back are legal.

Variations

Variations on these basic rules exist, particularly touch and flag football, which are designed as non-contact or limited-contact alternatives to the relative violence of regular American football. In touch and flag football, tackling is not permitted. Offensive players are "tackled" when a defender tags them or removes a flag from their body, respectively. Both of these varieties are played mainly in informal settings such as intramural or youth games. Another variation is "wrap", where a player is "tackled" when another player wraps his arms around the ball carrier. Professional, intercollegiate, and varsity-level high school football invariably use the standard tackling rules.

Another variation is with the number of players on the field. In sparsely populated areas, it is not uncommon to find high school football teams playing nine-man football, eight-man football or six-man football. Players often play on offense as well as defense. The Arena Football League is a league that plays eight-man football, but also plays indoors and on a much smaller playing surface.

Players

This diagram shows typical offensive and defensive formations. The offense (blue) consists of the quarterback (QB), fullback (FB), tailback (TB), wide receivers (WR), tight end (TE), and offensive linemen (C, OG, OT). The defense (red) consists of the defensive line (DL, DE), linebackers (LBs), cornerbacks (CB), strong safety (SS) and free safety (FS). Because teams can change any or all of the players between plays, the number of players at certain positions may differ on a given play. Here the offense is in the Normal I-Formation while the defense is in a 4-3 Normal.

Most football players have highly specialized roles. At the college and NFL levels, most play only offense or only defense.

Offense

• The offensive line (OL) consists of five players whose job is to protect the passer and clear the way for runners by blocking members of the defense. The lineman in the middle is the Center. Outside the Center are the Guards, and outside them are the Tackles. Except for the center, who snaps the ball to one of the backs, offensive linemen generally do not handle the ball.
• The quarterback (QB) receives the snap from the center on most plays. He then hands or tosses it to a running back, throws it to a receiver or runs with it himself. The quarterback is the leader of the offense and calls the plays that are signaled to him from the sidelines.
• Running backs (RB) line up behind or beside the QB and specialize in running with the ball. They also block, catch passes and, on rare occasions, pass the ball to others or even receive the snap. If a team has two running backs in the game, usually one will be a halfback (HB) or tailback (TB), who is more likely to run with the ball, and the other will usually be a fullback (FB), who is more likely to block.
• Wide receivers (WR) line up near the sidelines. They specialize in catching passes, though they also block for running plays or downfield after another receiver makes a catch.
• Tight ends (TE) line up outside the offensive line. They can either play like wide receivers (catch passes) or like offensive linemen (protect the QB or create spaces for runners). Sometimes an offensive lineman takes the tight end position and is referred to as a tackle eligible.^[10]

At least seven players must line up on the line of scrimmage on every offensive play. The other players may line up anywhere behind the line. The exact number of running backs, wide receivers and tight ends may differ on any given play. For example, if the team needs only 1 yard, it may use three tight ends, two running backs and no wide receivers. On the other hand, if it needs 20 yards, it may replace all of its running backs and tight ends with wide receivers.

Defense

In contrast to members of the offense, the rules of professional football (NFL Rulebook) and American college football NCAA Rulebook) do not specify starting position, movement, or coverage zones for members of the defensive team, except that they must be in the defensive zone at the start of play. The positions, movements and responsibilities of all defensive players are assigned by the team by selection of certain coverages, or patterns of placement and assignment of responsibilities. The positional roles are customary. These roles have varied over the history of American football. The following are customary defensive positions used in many coverages in modern American football.

• The defensive line consists of three to six players who line up immediately across from the offensive line. They try to occupy the offensive linemen in order to free up the linebackers, wreck the backfield of the offense, and tackle the running back if he has the ball before he can gain yardage or the quarterback before he can throw or pass the ball. They are the first line of defense.
• Behind the defensive line are the linebackers. They line up between the defensive line and defensive backs and may either rush the quarterback or cover potential receivers. Their main job is to cover the run up the middle.
• The last line of defense is known as the secondary, comprising at least three players who line up as defensive backs, which are either cornerbacks or safeties. They cover the receivers and try to stop pass completions. They occasionally rush the quarterback. However, this leaves the field wide open for passing.

Special teams

The units of players who handle kicking plays are known as special teams. Three important special-teams players are the punter, who handles punts, the placekicker or kicker, who kicks off and attempts field goals and extra points, and the long snapper, who snaps the ball for extra points, field goals, and punts. Also included on special teams are the returners. These players return punts or kickoffs and try to get in good field position. These players can also score touchdowns.

Uniform numbering

In the NFL, ranges of uniform numbers are (usually) reserved for certain positions:

• 1–9: Quarterbacks, kickers, and punters
• 10–19: Quarterbacks, kickers, punters, and wide receivers
• 20–49: Running backs and defensive backs
• 50–59: Centers and linebackers
• 60–79: Offensive and defensive linemen
• 80–89: Wide receivers and tight ends
• 90–99: Defensive linemen and linebackers

NCAA and high school rules specify only that offensive linemen must have numbers in the 50-79 range, but the NCAA "strongly recommends" that quarterbacks and running backs have numbers below 50 and wide receivers numbers above 79. This helps officials as it means that numbers 50 to 79 are ineligible receivers, or players that may never receive a forward pass. There are no numbering restrictions on defensive players in the NCAA, other than that no two players with the same jersey number can be on the field at the same time.

Basic strategy

Because the game stops after every down, giving teams a chance to call a new play, strategy plays a major role in football. Each team has a playbook of dozens to hundreds of plays. Ideally, each play is a scripted, strategically sound team-coordinated endeavor. Some plays are very safe; they are likely to get only a few yards. Other plays have the potential for long gains but at a greater risk of a loss of yardage or a turnover.

Generally speaking, rushing plays are less risky than passing plays. However, there are relatively safe passing plays and risky running plays. To deceive the other team, some passing plays are designed to resemble running plays and vice versa. These are referred to as play-action passes and draws. There are many trick or gadget plays, such as when a team lines up as if it intends to punt and then tries to run or pass for a first down. Such high-risk plays are a great thrill to the fans when they work. However, they can spell disaster if the opposing team realizes the deception and acts accordingly.

The defense also plans plays in response to expectations of what the offense will do. For example, a "blitz" (using linebackers or defensive backs to charge the quarterback) is often attempted when the team on defense expects a pass. A blitz makes downfield passing more difficult but exposes the defense to big gains if the offensive line stems the rush.

Many hours of preparation and strategizing, including film review by both players and coaches, go into the days between football games. This, along with the demanding physicality of football (see below), is why teams typically play at most one game per week.

Physicality

A halfback leads fellow backs through an agility drill at the Air Force Academy

American football is a collision sport. To stop the offense from advancing the ball, the defense must tackle the player with the ball by knocking or pulling him down. As such, defensive players must use some form of physical contact to bring the ball-carrier to the ground, within certain rules and guidelines. Tacklers cannot kick or punch the runner. They also cannot grab the face mask of the runner's helmet or lead into a tackle with their own helmet. Despite these and other rules regarding unnecessary roughness, most other forms of tackling are legal. Blockers and defenders trying to evade them also have wide leeway in trying to force their opponents out of the way. Quarterbacks are regularly hit by defenders coming on full speed from outside the quarterback's field of vision. This is commonly known as a blindside.

To compensate for this, players must wear special protective equipment, such as a padded plastic helmet, shoulder pads, hip pads and knee pads. These protective pads were introduced decades ago and have improved ever since to help minimize lasting injury to players. An unintended consequence of all the safety equipment has resulted in increasing levels of violence in the game. Players may now hurl themselves at one another at high speeds without a significant chance of injury. The injuries that do result tend to be severe and often season or career-ending and sometimes fatal. In previous years with less padding, tackling more closely resembled tackles in Rugby football. Better helmets have allowed players to use their helmets as weapons. This form of tackling is particularily unwise, due to the great potential for brain or spinal injury. All this has caused the various leagues, especially the NFL, to implement a complicated series of penalties for various types of contact. Most recently, virtually any contact with the helmet of a defensive player on the quarterback, or any contact to the quarterback's head, is now a foul.

Despite protective equipment and rule changes to emphasize safety, injuries remain very common in football. It is increasingly rare, for example, for NFL quarterbacks or running backs (who take the most direct hits) to make it through an entire season without missing some time to injury. Additionally, 28 football players, mostly high schoolers, died from direct football injuries in the years 2000-05 and an additional 68 died indirectly from dehydration or other examples of "non-physical" dangers, according to the National Center for Catastrophic Sport Injury Research.^[11] Concussions are common, with about 41,000 suffered every year among high school players according to the Brain Injury Association of Arizona.^[12]

Extra and optional equipment such as neck rolls, spider pads, rib protectors, and elbow pads help against injury as well, though they do not tend to be used by the majority of players due to their lack of requirement.

The danger of football and the equipment required to reduce it make regulation football impractical for casual play. Flag football and touch football are less violent variants of the game popular among recreational players.

Organization in the United States

Befitting its status as a popular sport, football is played in leagues of different size, age and quality, in all regions of the country. Organized football is played almost exclusively by men and boys, although a few amateur and semi-professional women's leagues have begun play in recent years.

Professional and semi-professional

The 32-team National Football League (NFL) is currently the only major professional American football league in North America. At least two new professional American Football Leagues are slated to begin playing in 2008, the All-American Football League and the United Football League. There are American football leagues located in over 50 countries in the world (see List of leagues of American and Canadian football). A few of the more popular international leagues are the German Football League (GFL) and the Japanese X-League. The NFL does not operate any developmental leagues currently since the folding of NFL Europa. Players unable to make an NFL team sometimes play in other leagues such as the Arena Football League or Canadian Football League, both of which have rules differing somewhat from those of the NFL.

University and collegiate

College football is also popular throughout North America. A majority of colleges and universities have football teams, often with dedicated football stadiums. These teams mostly play other similarly sized schools. The largest, most popular collegiate teams routinely fill stadiums larger than 75,000[2]. Four college football stadiums, The University of Michigan's Michigan Stadium, Penn State's Beaver Stadium, The University of Tennessee's Neyland Stadium and Ohio State's Ohio Stadium, seat more than 100,000 fans and usually sell out. The weekly autumn ritual of college football includes marching bands, cheerleaders, homecoming, parties, the tailgate party; it forms an important part of the culture in much of smalltown America. Football is generally the major source of revenue to the athletic programs of schools, public and private, in the United States.

High school

Most American high schools field football teams. Schools that are too small to field the minimum number of players play variants of football that specify six, seven, eight or nine players instead of the normal eleven. High school football is popular, especially in Texas, Florida, Ohio, Indiana, Illinois, California, Colorado, Pennsylvania, and the Southern United States, where many schools regularly fill stadiums holding over 10,000 fans, and can afford artificial playing surfaces^{[citation needed]}.

High school teams generally play only against other teams from their state (notable exceptions include matchups between nearby schools located on opposite sides of a state line and occasional matchups between two nationally-ranked teams for television purposes). Still, some private Christian high schools play for national championships through organizations like the Federated Christian Athletic Association

Youth leagues

Football is played recreationally by amateur and youth teams (e.g., the American Youth Football and Pop Warner little-league programs). There are also many "semi-pro" teams in leagues where the players are paid to play but at a small enough salary that they generally must also hold a full-time job.

Due to the speed and violence of the sport, many non-organized football games involve variations of the rules to minimize contact. These include touch football and flag football.

Calendar

Football is an autumn sport. A season typically begins in mid-to-late August and runs through December, into January. The professional playoffs run through January, and the Super Bowl is often played in the first week of February. The NFL draft is usually held in April, in which eligible college football players are selected by NFL teams, the order of selection determined by the teams' final regular season records.

It is a long-standing tradition in the United States (though not universally observed) that high school football games are played on Friday night, college games on Saturday, and professional games on Sunday. In the 1970s, the NFL began to schedule one game on Monday nights. Beginning in 2006, the NFL began scheduling games on Thursday and Saturday nights after the college football regular season concludes in mid-November, aired on the NFL Network. In recent years, nationally televised Thursday night college games have become a weekly fixture on ESPN, and most nights of the week feature at least one college game, though most games are still played on the traditional Saturday.

Certain fall and winter holidays—such as the NFL's Thanksgiving Classic and numerous New Year's Day college bowl games—have traditional football games associated with them.

Outside the United States

Outside the United States, the sport is referred to as "American football" (or a translation thereof) to differentiate it from other football codes. In Australia and New Zealand the game is known as Gridiron football, although in the United States the term gridiron refers only to the playing field itself.^[13] In much of the world, the term football is ambiguous and can refer to a number of different codes.

The NFL has attempted to introduce the game to other nations and operated a developmental league, NFL Europa, with teams in five German cities and one in the Netherlands, but this league folded following the 2007 season. The professional Canadian Football League and collegiate Canadian Interuniversity Sport play under the only slightly different Canadian rules.

In Japan, the X-League is a professional league with 60 teams in four divisions, using promotion and relegation. After the post-season playoffs, the X-League champion is determined in the Japan X Bowl. There are also over 200 universities fielding teams, with the national collegiate championship determined by the Koshien Bowl. The professional and collegiate champions then face each other in the Rice Bowl to determine the national champion.

In Germany, the German Football League whose elite division is called bundesliga, has 12 teams partitioned into north and south conferences. The finalists from the playoffs determine the German champion during the German Bowl.

The International Federation of American Football is the governing body for American football with 45 member associations from North and South America, Europe, Asia and Oceania. The IFAF also oversees the American Football World Cup, which is held every four years. Japan won the first two World Cups, held in 1999 and 2003. Team USA, which had not participated in the previous World Cups, won the title in 2007.

Despite this, the game has been slow to catch on in most countries. On October 2, 2005, the Arizona Cardinals and San Francisco 49ers played the first regular season NFL game outside of the United States, in Mexico City's Estadio Azteca.[3] In 2012, The United States Naval Academy will play the University of Notre Dame in Dublin, Ireland.