Football, American

I

Introduction

Football, American, distinct type of football that developed in the United States in the 19th century from association football and rugby football. It is one of the most popular American sports, attracting thousands of participants and millions of spectators annually.

The forerunner of all types of football may have been a game played by the ancient Greeks, called harpaston. In this game there was no limit to the number of players. The object was to move a ball across a goal line by kicking, throwing, or running with it. Classical literature contains detailed accounts of the game, including its rougher elements, such as ferocious tackling.

Most modern versions of football, however, originated in England, where a form of the game was known in the 12th century. In subsequent centuries football became so popular that various English monarchs, including Edward II and Henry VI, forbade the game because it took interest away from the military sport of archery. By the middle of the 19th century football had split into two distinct entities. Still popular today, these two sports include association football and rugby, in which players run with the ball and tackle. American football evolved out of these two sports.

II

The Playing Field and the Ball

The football playing field is rectangular, measuring 100 yd (110 m) long and 53.5 yd (48.9 m) wide. At both ends of the 100-yard dimension, white lines called goal lines mark off the entrances to the end zones. Each team defends one end zone. A team must carry, pass, or kick the ball into the 10-yd (9-m) end zone in the opponents' half of the field to score. Lines parallel to the end zones cross the field at 5-yd (4.5-m) intervals. These lines give the field a resemblance to a large gridiron. Another set of lines, known as the sidelines, runs along both sides of the field. In addition, two rows of lines, called hash marks, run parallel to the sidelines. The hash marks are 70 ft 9 in (21.6 m) from each sideline in the National Football League (NFL). Each play must begin on or between the hash marks. Before each play, the officials place the ball either between the hash marks or on the hash mark closest to the end of the previous play.

Situated in the middle of the rear line of each end zone are goalposts, consisting of a 10-ft (3-m) vertical pole topped by a horizontal crossbar from which two vertical upright posts extend, and which are 18 ft 6 in (about 5.6 m) apart.

The football consists of an inflated rubber bladder encased in a leather or rubber cover. The ball is an extended spheroid, having a circumference of 28.5 in (72.4 cm) around the long axis and 21.25 in (54 cm) around the short axis. It weighs between 14 and 15 oz (397 and 425 g).

III

Playing Time

A game of football is divided into four periods, known as quarters, each consisting of 15 minutes of playing time. The first two periods constitute the first half; the second two constitute the second half. Between the halves, a rest period, usually lasting about 15 minutes, is permitted the players, who may leave the field. The teams change halves of the field at the end of each quarter. The clocks stop at the end of each quarter and at certain other times, when particular events occur or when designated by the officials.

IV

The Players

Football is played by two opposing teams, each fielding 11 players. Each team tries to move the ball down the field to score in the end zone defended by its opponents. During a football game the teams are designated as the offensive team (the team in possession of the ball) and the defensive team (the team defending a goal line against the offensive team). Players involved in kicking situations are known as the special teams. The 11 players of the offensive team are divided into two groups: 7 linemen, who play on the line of scrimmage (an imaginary line designating the position of the ball) and a backfield of 4 players, called backs, who stand in various positions behind the linemen. The lineman whose position is in the middle of the line is called the centre. On his left is the left guard and on his right is the right guard. On the left of the left guard is the left tackle, and on the right of the right guard is the right tackle; similarly, on the ends of the line are the tight end and the split end. The back who usually stands directly behind the centre and directs the play of the offensive team is known as the quarterback. Teams often use wide receivers in the place of tight ends, split ends, half-backs, or fullbacks. Wide receivers line up on the line of scrimmage but wide of the rest of the formation.

The defensive team consists of a row of linemen, who comprise the defensive line, a row of linebackers, and a collection of defensive backs, known as the secondary. The defensive line can use any number of players, though most teams use three or four linemen. Defensive linemen principally are responsible for stopping the opposition's rushing attack and, in passing situations, putting pressure on the quarterback. The linebackers line up behind the defensive line and, depending on the situation, are used to stop runners, to pressurize the quarterback, or to cover the opposition's receivers. Teams usually employ three or four linebackers. The secondary is comprised of cornerbacks, who cover wide receivers, and safeties, who cover receivers, offer support in stopping the rushing attack, and pressurize the quarterback. The secondary commonly consists of two cornerbacks and two safeties.