The national fall (autumn) and winter sport in the USA, played between September and January. It resembles rugby, but forward passing of the ball is permitted. It is played on a rectangular field 360 ft (110 m) by 160 ft (49 m), divided into 5-yd (4·6-m) segments which give the field a gridiron effect. The object is to score touchdowns - the moving of the ball across the goal line in a running or passing play. This is similar to the try in rugby, but progress has to be made upfield by a series of plays, and a team must make 10 yd (9·1 m) of ground within four plays, otherwise it loses possession of the ball. Six points are awarded for a touchdown and one point for a conversion (kicking the ball between the posts and over the crossbar), as in rugby. A goal kicked from anywhere on the field (a field goal) is worth 3 points. Teams consist of more than 40 squad members, but only 11 are allowed on the field for each team at any one time. Special units come on for specific roles. When a team is attacking, the 11 players will be different from those on the field when they are on the defence. The game was first played in US colleges in the mid-19th Century , and the first rules were drawn up at Princeton College in 1867. The professional game in the USA comes under the auspices of the National Football League, which is divided into the American Football Conference (AFC) and National Football Conference (NFC). The leading teams of the two conferences meet in a series of play-off games each January for the Super Bowl (instituted 1966–7).