Gridiron football (), also known as North American football, or in North America as simply football, is a family of football team sports primarily played in the United States and Canada. American football, which uses 11 players, is the form played in the United States and the best known form of gridiron football worldwide, while Canadian football, which uses 12 players, predominates in Canada. Other derivative varieties include arena football, flag football and amateur games such as touch and street football. Football is played at professional, collegiate, high school, semi-professional, and amateur levels.
These sports originated in the 19th century out of older games related to modern rugby football, more specifically rugby union football. Early on, American and Canadian football developed alongside (but independently from) each other; the root of the game known as "football" today originates with an 1874 game between Harvard and McGill Universities, following which the American school adopted the Canadian school's more rugby-like rules.Over time, Canadian teams adopted features of the American variant of the game and vice versa. Both varieties are distinguished from other football sports by their use of hard plastic helmets and shoulder pads, the forward pass, the system of downs, a number of unique rules and positions, measurement in customary units of yards (even in Canada, which largely metricated in the 1970s), and a distinctive brown leather ball in the shape of a prolate spheroid with pointed ends.
The international governing body for the sport is the International Federation of American Football (IFAF); although the organization plays all of its international competitions under American rules, it uses a definition of the game that is broad enough that it includes Canadian football under its umbrella, and Football Canada (the governing body for Canadian football) is an IFAF member.
