The Rules of American Football

Each football league adopts its own rules, which cover a wide range of subjects including equipment, uniforms, player eligibility, and behaviour of personnel on the sidelines. The following synopsis covers only the rules governing on-field play of the game, and even so some details may vary from one league to another. Also, this summary covers only the most common situations, and not every contingency that may arise in a game.

Objective

Like most other games of football, the object of American football is to advance the ball towards the opponent's end of the field and score more points than the opposing team within a set time limit.

Field and Players

The American football field is often called the gridiron because the markings on the field resemble that type of grill that can be used to cook food over a fire. The game is played on a rectangular field 120 yards long by 53-1/3 yards wide. The longer boundary lines are sidelines, while the shorter boundary lines are end lines. Near each end of the field is a goal line; they are 100 yards apart. A scoring area called an end zone extends 10 yards beyond each goal line to each end line.

Yard lines cross the field every 5 yards, and are numbered from each goal line to the 50-yard line, or midfield (similar to a typical rugby league field). Two rows of lines, known as hash marks, parallel the side lines near the middle of the field. All plays start with the ball on or between the hash marks.

At the back of each end zone are two goal posts (also called uprights) that are 18.5-feet apart. The posts are connected by a crossbar 10 feet from the ground. Successful kicks must go above the crossbar and between the uprights.

Each team has 11 players on the field at a time. However, teams may substitute for any or all of their players between plays. As a result, players have very specialised roles, and almost all of the 53 players on an NFL team will play in any given game. Thus, teams are divided into three separate units: the offensive team, the defensive team, and the special teams.

Game Duration

A standard football game consists of four 15-minute quarters, with a halftime after the second quarter. However, the clock stops after certain plays, so a game can last more than three hours in real time. If an NFL game is tied after four quarters, the teams play up to another 15 minutes. The first team that scores wins; if neither team scores, the game is a tie. College overtime rules are more complicated.

Advancing the Ball

Advancing the ball in American football resembles the six-tackle rule and the play-the-ball in rugby league football. The team that takes possession of the ball (the offense) has four attempts (called downs) to advance the ball 10-yards towards their opponent's end zone. When the offense gains 10-yards, it gets a first down, or another four downs to gain 10-yards. If the offense fails to gain a first down, it loses possession of the ball.

A snap is how the ball is returned to play. All players line up facing each other at the line of scrimmage (the position on the field where the play begins). The play then begins when one offensive player, the centre, passes, or snaps the ball under his legs to a teammate, almost always the quarterback.

Players can then advance the ball in two ways:

By running with the ball, also known as rushing.
By throwing the ball to a teammate, known as passing.

A play or down ends, and the ball becomes dead, after any of the following:

The player with the ball is tackled by a member of the other team, the defense. (Note: In American sporting terminology, the emphasis is on the first syllable: DE-fense, not de-FENSE.) In the NFL, a player is tackled when any part of their body above the knee, except the hand, touches the ground after contact by an opposing player (except for a player who is kneeling to hold the ball for a place kick). In college football, the ball is dead if a player's body (except for a hand or foot) touches the ground, regardless of whether the opposing team may contact with him.
A pass thrown forward touches the ground before it is caught. This is known as an incomplete pass, and the ball is returned to the spot where the previous play began. Note that if the ball is not in the possession of any player and touches the ground for any reason other than an incomplete forward pass, this is considered a fumble and the ball remains in play.
The ball or the player with the ball goes beyond the dimensions of the field (out of bounds).
A team scores.
On a kicking play, a receiving player catches the ball after signalling for a fair catch.
On a punt, a member of the kicking team touches ("downs") the ball before it is touched by any member of the receiving team.

Changes of Possession

The offense maintains possession of the ball unless one of the following things happens:

The team fails to get a first down, that is, on a fourth down play it fails to advance the ball at least 10 yards from where it was spotted on first down. The defensive team takes over the ball at the spot where the play ends.
The offense scores a touchdown or field goal. The team that scored then kicks off the ball to the other team.
The offense punts the ball to the defense. A punt is a kick in which a player drops the ball and kicks it before it hits the ground. Punts are nearly always made on fourth down, when the offensive team does not want to risk giving up the ball to the other team at its current spot on the field (through a failed attempt to convert the fourth down) and feels it is too far from the other team's goal posts to kick a field goal. (Punts on earlier downs are extremely rare, usually performed as a trick play or in extremely adverse weather conditions.)
A defensive player catches a forward pass. This is called an interception, and the player who makes the interception can run with the ball until tackled or forced out of bounds.
An offensive player drops the ball (a fumble), and a defensive player picks it up. As with interceptions, a player recovering a fumble can run with the ball until tackled or forced out of bounds. Lost fumbles and interceptions are together known as turnovers.
The offensive team misses a field goal attempt. The other team gets the ball at the spot where the previous play began (or, in the NFL, at the spot of the kick). If the unsuccessful kick was attempted from very close to the end zone, the other team gets the ball at its own 20-yard line (that is, 20 yards from the end zone).
An offensive player is tackled or forced out of bounds in their own end zone. This rare occurrence is called a safety, and the offense must then free kick (usually in the form of a punt) the ball to the other team from its own 20-yard line.

However, if a defensive player gains possession of the ball in their own end zone (by intercepting a pass, recovering a fumble, or receiving a kick) and goes out of bounds, is tackled, or simply puts their knee to the ground without having crossed the goal line, this is a "touchback," not a safety; the team that recovered the ball retains possession and may put it into play from its own 20-yard line. Also, a touchback occurs if a kicked ball crosses the goal line and then leaves the end zone untouched.

Scoring

A team scores points by the following plays:

A touchdown is worth 6 points. A touchdown is scored when a player runs the ball into or catches a pass in their opponent's end zone.

After a touchdown, the scoring team attempts a conversion. The ball is placed at the other team's 3-yard-line (the 2-yard-line in the NFL). The team can attempt to kick it over the crossbar and through the goal posts for 1 point (an extra point), or run or pass it into the end zone for 2 points (a two-point conversion).

A field goal is worth 3 points, and it is scored by kicking the ball on a play from scrimmage over the crossbar and through the goal posts. Field goals must be place-kicked, that is, kicked when the ball is held vertically against the ground by a teammate. A field goal is usually attempted on fourth down instead of a punt when the ball is close to the goal line.
A safety is worth 2 points. A safety is scored by the defense when the ball goes out of bounds in the offensive team's end zone (except as the result of an incomplete pass), or the ball carrier is tackled in the offensive team's end zone. In the NFL, certain penalties by the offense occurring in the end zone also result in a safety. The team that had possession of the ball must then free kick (a kickoff-like play in which the ball is kicked like a punt) to the other team from the 20-yard line.

Kickoffs

Each half begins with a kickoff. Teams also kick off after scoring touchdowns and field goals. The ball is kicked from a kicking tee, which is placed on one's own 30-yard line in the NFL and on the 35-yard line in college football. The other team's kick returner tries to catch the ball and advance it as far as possible. Where they are stopped is the point where the offense will begin its drive, or series of offensive plays. If the kick returner catches the ball in their own end zone, they can either run with the ball, or elect for a touchback by kneeling in the end zone. The receiving team can then start its offensive drive from its own 20-yard line. A touchback can also occur when the kick goes out of the end zone. Punts can also end in touchbacks.

Passing

One feature that distinguishes American and Canadian football from other football sports is the forward pass. The offense can throw the ball forward only once on a play and only from behind the line of scrimmage. The ball can be thrown sideways or backwards at any time. However, such passes are much rarer in American football than in rugby.