A football is a ball inflated with air that is used to play one of the various sports known as football. In these games, with some exceptions, goals or points are scored only when the ball enters one of two designated goal-scoring areas; football games involve the two teams each trying to move the ball in opposite directions along the field of play.
The first balls were made of natural materials, such as an inflated pig bladder, later put inside a leather cover, which has given rise to the American slang-term "pigskin". Modern balls are designed by teams of engineers to exacting specifications, with rubber or plastic bladders, and often with plastic covers. Various leagues and games use different balls, though they all have one of the following basic shapes:
- a sphere: used in Association football and Gaelic football
- a prolate spheroid
The precise shape and construction of footballs is typically specified as part of the rules and regulations.
The oldest football still in existence, which is thought to have been made circa 1550, was discovered in the roof of Stirling Castle, Scotland, in 1981. The ball is made of leather (possibly from a deer) and a pig's bladder. It has a diameter of between 14–16 cm (5.5–6.3 in), weighs 125 g (4.4 oz) and is currently on display at the Smith Art Gallery and Museum in Stirling.
American and Canadian football
In Canada and the United States, the term football usually refers to a ball made of cow hide leather, which is required in professional and collegiate football. Footballs used in recreation, and in organised youth leagues, may be made of rubber or plastic materials (the high school football rulebooks still allow the inexpensive all-rubber footballs, though they are less common than leather). Since 1941, Wilson  has been the exclusive supplier of leather for National Football League footballs. The arrangement was established by Arnold Horween, who had played and coached in the NFL. Horween Leather Company also supplies leather to Spalding, supplier of balls to the Arena Football League.
Leather panels are typically tanned to a natural brown color, which is usually required in professional leagues and collegiate play. At least one manufacturer uses leather that has been tanned to provide a "tacky" grip in dry or wet conditions. Historically, white footballs have been used in games played at night so that the ball can be seen more easily; however, improved artificial lighting conditions have made this no longer necessary. At most levels of play (but not, notably, the NFL), white stripes are painted on each end of the ball, halfway around the circumference, to improve nighttime visibility and also to differentiate the college football from the pro football. However, the NFL once explored the usage of white-striped footballs – in Super Bowl VIII.
In the CFL the stripes traverse the entire circumference of the ball. The UFL used a ball with lime-green stripes. The XFL used a novel color pattern, a black ball with red curved lines in lieu of stripes, for its footballs; this design was redone in a tan and navy color scheme for the Arena Football League in 2003. Two indoor American football leagues, the Ultimate Indoor Football League and American Indoor Football, use a ball with red, white and blue panels.
Law 2 of the game specifies that the ball is an air-filled sphere with a circumference of 68–70 cm (27–28 in), a weight of 410–450 g (14–16 oz), inflated to a pressure of 0.6 to 1.1 atmospheres (60–111 kPa or 8.7–16.1 psi) "at sea level", and covered in leather or "other suitable material". The weight specified for a ball is the dry weight, as older balls often became significantly heavier in the course of a match played in wet weather. The standard ball is a Size 5, although smaller sizes exist: Size 3 is standard for team handball and Size 4 in futsal and other small-field variants. Other sizes are used in underage games or as novelty items.
Most modern Association footballs are stitched from 32 panels of waterproofed leather or plastic: 12 regular pentagons and 20 regular hexagons. The 32-panel configuration is the spherical polyhedron corresponding to the truncated icosahedron; it is spherical because the faces bulge from the pressure of the air inside. The first 32-panel ball was marketed by Select in the 1950s in Denmark. This configuration became common throughout Continental Europe in the 1960s, and was publicised worldwide by the Adidas Telstar, the official ball of the 1970 World Cup.
There are a number of different types of football balls depending on the match and turf including: training footballs, match footballs, professional match footballs, beach footballs, street footballs, indoor footballs, turf balls, futsal footballs and mini/skills footballs.
Australian rules football
The football used in Australian football is similar to a rugby ball but generally slightly smaller and more rounded at the ends, but more elongated in overall appearance, being longer by comparison with its width than a rugby ball. A regulation football is 720–730 millimetres (28–29 in) in circumference, and 545–555 mm (21.5–21.9 in) transverse circumference, and inflated to a pressure of 62–76 kPa (9.0–11.0 psi). In the AFL, the balls are red for day matches and yellow for night matches.
The first games of Australian football were played with a round ball, because balls of that shape were more readily available. In 1860, Australian football pioneer Tom Wills argued that the oval rugby ball travelled further in the air and made for a more exciting game. It became customary in Australian football by the 1870s.
The Australian football ball was invented by T. W. Sherrin in 1880, after he was given a misshapen rugby ball to fix. Sherrin designed the ball with indented rather than pointy ends to give the ball a better bounce.
Gaelic football is played with a spherical leather ball, roughly 25 cm (9.8 in) in diameter and 69–74 cm (27–29 in) in circumference. A dry ball weighs between 370 and 425 g (13.1 and 15.0 oz). The pattern of panels is identical to the volleyball, consisting of six groups perpendicular to each other, each group being composed of two trapezoidal panels and one rectangular panel; 18 panels in all.
Gaelic footballs are also the standard balls used in international rules football.
Gaelic football has been played with a round ball since the game was first organised in 1887, balls made by the Irish sports company O'Neills have been used since the company was founded in 1918 and are recognised as the official ball to be played with, although it is now permitted to use the ball manufactured by the Irish sports company Gaelic Gear.
Until 1870, rugby was played with a near spherical ball with an inner-tube made of a pig's bladder. In 1870 Richard Lindon and Bernardo Solano started making balls for Rugby school out of hand stitched, four-panel, leather casings and pigs’ bladders. The rugby ball's distinctive shape is supposedly due to the pig’s bladder, although early balls were more plum-shape than oval. The balls varied in size in the beginning depending upon how large the pig’s bladder was. Because of the pliability of rubber the shape gradually changed from a sphere to an egg. In 1892 the RFU endorsed ovalness as the compulsory shape. The gradual flattening of the ball continued over the years. The introduction of synthetic footballs over the traditional leather balls, in both rugby codes, was originally governed by weather conditions. If the playing surface was wet, the synthetic ball was used, because it wouldn't absorb water and become heavy. Eventually, the leather balls were phased out completely.
Rugby league is played with a prolate spheroid shaped football which is inflated with air. A referee will stop play immediately if the ball does not meet the requirements of size and shape. Traditionally made of brown leather, modern footballs are synthetic and manufactured in a variety of colours and patterns. Senior competitions should use light-coloured balls to allow spectators to see the ball more easily. The football used in rugby league is known as "international size" or "size 5" and is approximately 27 cm (11 in) long and 60 cm (24 in) in circumference at its widest point. Smaller-sized balls are used for junior versions of the game, such as "Mini" and "Mod". A full size ball weighs between 383 and 440 g (13.5 and 15.5 oz). Rugby league footballs are slightly more pointed than rugby union footballs and larger than American footballs.
The ball used in rugby union, usually referred to as a rugby ball, is a prolate spheroid essentially elliptical in profile. Traditionally made of brown leather, modern footballs are manufactured in a variety of colors, patterns. A regulation football is 28–30 cm (11–12 in) long and 58–62 cm (23–24 in) in circumference at its widest point. It weighs 410–460 g (14–16 oz) and is inflated to 65.7–68.8 kPa (9.5–10.0 psi).
In 1980, leather-encased balls, which were prone to water-logging, were replaced with balls encased in synthetic waterproof materials. The Gilbert Synergie was the match ball of the 2007 Rugby World Cup.
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