the national sport. Other nations from the South Pacific and Europe also play in the Pacific Cup and European Cup respectively. The premier international competition is the Rugby League World Cup, which is contested quadrennially. The premier international club comeptition is the World Club Challenge, which is contested annually in February. Currently there are two major domestic professional leagues globally: National Rugby League: Australia (16 teams) New Zealand (1 team) Super League: England (11 teams) France (1 team) Wales (currently no teams, part of system) Gridiron Football In Canada and the United States, rugby developed into gridiron football. During the late 1800s (and even the early 1900s), the two forms of the game were very similar (to the point where the United States was able to win the gold medal for rugby union at the 1920 and 1924 Summer Olympics), but numerous rule changes have differentiated the gridiron-based game from its rugby counterpart, introduced by Walter Camp in the United States and John Thrift Meldrum Burnside in Canada. Among unique features of the North American game are the separation of play into downs instead of releasing the ball immediately upon tackling the requirement that the team with the ball set into a set formation for at least one second before resuming play after a tackle (and the allowance of up to 40 seconds to do so) the allowance for one forward pass from behind the site of the last tackle on each down the evolution of hard plastic equipment (particularly the football helmet and shoulder pads) a smaller and pointier ball that is favorable to being passed but makes drop kicks impractical a generally smaller and narrower field measured in customary units instead of metric (in some variants of the American game a field can be as short as 50 yards between end zones) a distinctive field (shaped like a gridiron, from which the code's nickname is derived) with lines marked in five-yard intervals Worldwide, there are two major professional leagues of gridiron football, both domestic: National Football League: United States (32 teams) Canadian Football League: Canada (9 teams) Rules Distinctive features common to both rugby codes include the use of an oval ball and the prohibition of the forward pass. Due to the prohibition, players can gain ground only by running with the ball or by kicking it. Furthermore, unlike American and Canadian football, neither league nor union players