American football - rules

American football - rules

Gameplay

American football is played between two teams of 11 players each, with an oval (specifically prolate spheroid) ball. The basic format of the game involves two teams, one of which is in possession of the ball. The team in possession of the ball, termed the offense, tries to advance the ball towards the end zone, the scoring area at either end of the field. The other team, termed the defense, tries to stop the offense and prevent them from advancing the ball. A game begins with a kickoff; the kicking and receiving teams are determined by a pre-game coin toss. The kickoff occurs as a player on the kicking team (the placekicker) kicks the ball from a tee. The receiving team then catches the ball and runs towards the opposing end zone until they are tackled or step out of bounds, at which point the ball is considered dead. The point where the ball becomes dead is defined as the first line of scrimmage, and play begins from that point.

Teams and positions

A game is played between two teams of 11 players each; having less players on the field is legal, but playing with more on the field is punishable by a penalty. Teams may substitute any number of their players between downs, and the game in general has developed a system where teams have different offensive, defensive and special teams squads. This system is a vital aspect of the modern game and replaced the old system, where only limited substitution was allowed. Individual players in a football game must be designated with a uniform number which is between 1 and 99; in the NFL, teams are required to number their players by a league-approved numbering system during the regular season and any exceptions must be approved by the Commissioner, while in the NCAA and NFHS teams are "strongly advised" to number their offensive players according to a league-suggested numbering scheme.

Offensive unit

The role of the offensive unit is to advance the ball down the field, with the ultimate goal of scoring a touchdown.
In football, the offensive team must line up in a legal formation before they can snap the ball. An offensive formation is considered illegal if there are more than four players in the backfield or there are less than five players numbered 50-79 on the offensive line; Players can line up in a position whose eligibility is different than their number permits, provided they immediately report the change to the referee, who will inform the defensive team of the change. The player must continue playing in that position until play has been stopped by a timeout, challenge or foul, the two-minute warning, the end of the quarter, a score by either team, a change in possession between the teams, or if the player withdraws for one play. Neither team's players (with the exception of the snapper) are allowed to line up or cross the neutral zone until the ball is snapped. Additionally, interior offensive linemen are not allowed to move until the ball is snapped.

Defensive unit

A group of defensive players for the Dallas Cowboys forcing Houston Texans running back Arian Foster to fumble the ball.
The role of the defense is to prevent the offense from scoring by tackling the ball carrier or by forcing turnovers (interceptions or fumbles).

Equipment

American football is a violent game and players wear armor-like padding to protect themselves. At minimum, players wear a protective football helmet, which has a face mask, and a set of shoulder pads, though different leagues may also require additional padding, including thigh pads/guards, knee pads, chest protectors and mouth guards. College and high school play require the use of a mouthguard. Despite these protections, injuries do occur - particularly concerning are head injuries such as concussions. Concussions are often caused by helmet-to-helmet or upper-body contact between opposing players, although the helmets have prevented more serious injuries such as skull fractures.

Rules

The rules of American football vary somewhat from league to league, but each level of the sport has a prominent, national body which determines a unified code of rules for that level of play. The National Football League (NFL) is the highest level of professional football in the United States. The National Collegiate Athletic Association (NCAA), which manages university athletics in the United States for most colleges and universities, maintains the rules for college football, while high school football is overseen by the National Federation of State High School Associations (NFHS). The largest organization for youth football (younger than high school age) is Pop Warner Little Scholars.

Scoring

Scoring can be accomplished in several ways in American football. A touchdown, worth six points, is the most valuable scoring play; a touchdown is scored when the ball is advanced into, caught or collected in the end zone of the opposing team. Following a touchdown, the scoring team has the chance to score more points through a try (more commonly known as the PAT, meaning point(s)-after-touchdown), a single opportunity to score points. A PAT is attempted by the offense from the two-yard or three-yard line (depending on the level of play), and is worth one point (called the extra point) if scored by a field goal and two points (called the two-point conversion) if scored by what would normally be a touchdown. If the attempt fails, no extra points are awarded. A field goal, worth three points, is scored when the ball is placekicked or dropkicked through the uprights and over the crossbars of the defense's goalposts. A safety, worth two points for the defense, is scored when the ballcarrier is tackled in his own end zone.

Field

Football games are played on a rectangular field measuring 120 yards (109.7 meters) long and 53.3 yards (48.7 meters) wide. Lines are placed along both the ends and sides of the field (known as end lines and side lines, respectively), and goal lines are marked 10 yards outward from each end line. Weighted pylons are placed on the inside corner of the intersections of the goal lines and end lines. White markings on the field serve to identify the length out from the end zone; these lines include inbound lines (or hash marks), short parallel lines which mark off one-yard increments and that are placed along the sidelines as well as either 70 feet, 9 inches or 60 feet out from the sidelines (depending on the level of play), yard lines, continuous lines running from one end of the field to the other, and a one-yard-long line placed at the center of the two-yard-lines (in professional play) or three-yard-lines (in college play) at both ends of the field. Numerical marks indicating the yard lines in multiples of 10 are placed along both sides of the field.

Goalposts are placed at the center of the plane of each of the two end lines; the crossbar of these posts (measuring 18 feet, 6 inches or 5.64 meters in professional and college play and 23 feet, 4 inches or 7.1 meters in high school play) is placed 10 feet above the ground, while the uprights on both ends of the crossbar are extended 30 feet (9.1 meters) in professional fields, a minimum of 30 feet in college fields, and a minimum of 10 feet (3.1 meters) in high school fields.Padding is placed around the base of the goal post, and oranged-colored ribbons are normally placed at the tip of both uprights.

Duration and time stoppages

Football games last a total of 60 minutes in professional and college play, divided into two halves of 30 minutes and four quarters of 15 minutes. In high school football, games are 48 minutes in length with two halves of 24 minutes and four quarters of 12 minutes. The two halves are separated by a halftime period, while the first and third quarters are also followed by a short break. Games last longer than their defined length due to play stoppages, with the average NFL game lasting just over 3 hours. Teams switch goals following the first and third quarters. If a down is in progress and a quarter ends, play continues until the down is completed.

Time in a football game is measured by the game clock. An operator is responsible for starting, stopping and generally operating the game clock; the operator does so based on the direction of the appropriate official. A separate clock, the play clock, is used to determine if a delay of game infraction has been committed. If the play clock expires before the ball has been snapped or free-kicked, a delay of game foul is called on the offense. The play clock is set to 40 seconds in professional and college football, and to 25 seconds in high school play or following certain administrative stoppages in the former levels of play.

Source: www.en.wikipedia.org