The following is a description of the various and alternating rules of gridiron football. Numerous leagues or organizations tend to send a laundry list of rules in order to better distinguish themselves from their counterparts.
American football (general)
Field and players American football is played on a football field that is . The longer boundary lines are sidelines, while the shorter boundary lines are end lines. Sidelines and end lines are out of bounds. Near each end of the field is a goal line; they are apart. A scoring area called an end zone extends beyond each goal line to each end line. The end zone includes the goal line but not the end line. While the playing field is effectively flat, it is common for a field to be built with a slight crown—with the middle of the field higher than the sides—to allow water to drain from the field.
Yard lines cross the field every , and are numbered every 10 yards from each goal line to the 50-yard line, or midfield (similar to a typical rugby league field). Two rows of short lines, known as inbounds lines or hash marks, run at 1-yard (91.4 cm) intervals perpendicular to the sidelines near the middle of the field. All plays start with the ball on or between the hash marks. Because of the arrangement of the lines, the field is occasionally referred to as a gridiron.
At the back of each end zone are two goalposts (also called uprights) connected by a crossbar from the ground. For high skill levels, the posts are apart. For lower skill levels, these are widened to .
Each team has 11 players on the field at a time. However, teams may substitute for any or all of their players, if time allows, during the break between plays. As a result, players have very specialized roles, and, sometimes (although rarely) almost all of the (at least) 46 active players on an NFL team will play in any given game. Thus, teams are divided into three separate units: the offense, the defense and the special teams.
Start of halves Similarly to association football, the game begins with a coin toss to determine which team will kick off to begin the game and which goal each team will defend. The options are presented again to start the second half; the choices for the first half do not automatically determine the start of the second half (i.e. it is possible for the same team to kick off both halves). But, this ordinarily does not happen. Normally, the two halves are not both kicked off by the same team. The referee conducts the coin toss with the captains (or sometimes coaches) of the opposing teams. The team that wins the coin toss has three options: They may choose whether to kick or receive the opening kickoff. They may choose which goal to defend. They may choose to defer the first choice to the other team and have first choice to start the second half. Whatever the first team chooses, the second team has the option on the other choice (for example, if the first team elects to receive at the start of the game, the second team can decide which goal to defend).
At the start of the second half, the options to kick, receive, or choose a goal to defend are presented to the captains again. The team which did not choose first to start the first half (or which deferred its privilege to choose first) now gets first choice of options.
Game duration A standard football game consists of four 15-minute quarters (12-minute quarters in high-school football and often shorter at lower levels, usually one minute per grade [e.g. 9-minute quarters for freshman games]), with a 12-minute half-time intermission (30 minutes in the Super Bowl) after the second quarter in the NFL (college halftimes are 20 minutes; in high school the interval is 15 or 20 minutes; 10 minutes for lower grades). The clock stops after certain plays; therefore, a game can last considerably longer (often more than three hours in real time), and if a game is broadcast on television, TV timeouts are taken at certain intervals of the game to broadcast commercials outside of game action. If an NFL game is tied after four quarters, the teams play an additional period, timed like the fourth quarter, lasting up to 10 minutes. There is a coin toss in the NFL just like the beginning of the game. If the receiving team scores a safety during the possession, the game is over & they win. If they kick a field goal, then the other team gets a possession. If they score a touchdown, they win. If they tie the score by kicking a field goal, then whoever scores next wins. If the team with the first possession turns the ball over without scoring any points, then the first team to score, wins. If the defense scores a touchdown through an interception or fumble recovery, or they get a safety, then they win. In a regular-season NFL game, if no one scores in the overtime, the game ends tied. In an NFL playoff game, multiple 15-minute overtime periods are played, as needed, to determine a winner. These periods are timed as if a game had started over. Since the 2022 playoffs & 2025 regular season, teams will be guaranteed one possession to start first overtime. In the extremely rare case a game would go as far as a third OT—which has never happened in the NFL—there would be no "halftime intermission"; play would resume with a kickoff similar to a normal third quarter.
No overtime is played in NFL preseason up to & since .
College overtime rules are more complicated and are described in Overtime (sport).
Advancing the ball Advancing the ball in American football resembles the six-tackle rule and the play-the-ball in rugby league. The team that takes possession of the ball (the offense) has four attempts, called downs, in which to advance the ball toward their opponent's (the defense's) end zone. When the offense succeeds in gaining at least 10 yards, it gets a first down, meaning the team has another set of four downs to gain yet another 10 yards or to score. If the offense fails to gain a first down (10 yards) after 4 downs, the other team gets possession of the ball at the point where the fourth down ended, beginning with their first down to advance the ball in the opposite direction.
Except at the beginning of halves and after scores, the ball is always put into play by a snap. Offensive players line up facing defensive players at the line of scrimmage (the position on the field where the play begins). One offensive player, the center, then passes (or "snaps") the ball backwards between his legs to a teammate behind him, usually 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 a forward pass or as passing the football. The forward pass is a key factor distinguishing American and Canadian football from other football sports. The offense can throw the ball forward only once during a down and only from behind the line of scrimmage. The ball can be thrown, pitched, handed-off, or tossed sideways or backwards at any time.
A down ends, and the ball becomes dead, after any of the following: The player with the ball is forced to the ground (a tackle) or has his forward progress halted by members of the other team (as determined by an official). A forward pass flies beyond the dimensions of the field (out of bounds) or touches the ground before it is caught. This is known as an incomplete pass. The ball is returned to the most recent line of scrimmage for the next down. The ball or the player with the ball goes out of bounds. A team scores.
Officials blow a whistle to notify players that the down is over.
Before each down, each team chooses a play, or coordinated movements and actions, that the players should follow on a down. Sometimes, downs themselves are referred to as "plays."
Change of possession The offense maintains possession of the ball unless one of the following things occurs: The team fails to get a first down— i.e., in four downs they fail to move the ball past a line 10 yards ahead of where they got their last first down (it is possible to be downed behind the current line of scrimmage, losing "yardage"). The defensive team takes over the ball at the spot where the 4th-down play ends. A change of possession in this manner is commonly called a turnover on downs, but is not credited as a defensive "turnover" in official statistics. Instead, it goes against the offense's 4th down efficiency percentage. The offense scores a touchdown or field goal. The team that scored then kicks the ball to the other team in a special play called a kickoff. 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 (though see quick kick), 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 make a first down) and feels it is too far from the other team's goal posts to attempt a field goal. 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 he is tackled, forced out of bounds, or scores. 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, forced out of bounds, or scores. Backward passes that are not caught do not cause the down to end like incomplete forward passes do; instead the ball is still live as if it had been fumbled. Lost fumbles and interceptions are together known as turnovers. The offensive team misses a field goal attempt. The defensive 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 within of the end zone, the other team gets the ball at its own 20-yard line (that is, 20 yards from the end zone). If a field goal is missed or blocked and the ball remains in the field of play, a defensive player may pick up the ball and attempt to advance it. While in his own end zone, an offensive ball carrier is tackled, forced out of bounds, loses the ball out of bounds, or the offense commits certain fouls. This fairly rare occurrence is called a safety. An offensive ball carrier fumbles the ball forward into the opposing end zone, and then the ball goes out of bounds. This extremely rare occurrence leads to a touchback, with the ball going over to the opposing team at their 20-yard line (Note that touchbacks during non-offensive special teams plays, such as punts and kickoffs, are quite common).
Scoring 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. Unlike rugby, a player does not have to touch the ball to the ground to score; a touchdown is scored any time a player has possession of the ball but not while the ball is on or beyond the opponents' goal line (or the plane above it). After a touchdown, the scoring team attempts a try (which is also analogous to the conversion in rugby). The ball is placed at the other team's line (the line in the NFL on 2-point conversions or for 1-point conversions). 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)), 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, the NFL, USFL and Texas high school football, if the defense intercepts or recovers a fumble during a one or two-point conversion attempt and returns it to the opposing end zone, the defensive team is awarded the two points.