American football, known in the United States simply as football ("soccer" in Portuguese), and some other English speaking countries such as gridiron, is a team sport and contact that arose from a variation of rugby and that rewards speed, agility, tactics and brute force of the players that push, block and chase each other, trying to advance a ball in enemy territory for an hour of game time, which becomes three or four real time. We often see in a football metaphor for war, with much personal violence taking place within the camp, with players weighing 150 pounds or more to push each other with every ounce of their weight, and with a clearly defined front line , which moves back and forth along the field, separating the teams attack and defense.
American football in its current form arose from a series of three games between Harvard and Yale, Mackenzie, in 1867. McGill players played under the rules of rugby, while playing the game of puc Boston, closer to European football. As often happens in these times of almost no universal rules, the teams played with alternating rules so that both had a fair chance of winning. The Harvard players liked having a chance to run with the ball, and em1875 convinced Yale to adopt the rules of rugby for the annual game between the two universities. In 1876, Yale, Harvard, Princeton and Columbia formed the Football Association Inter-university (Intercollegiate Football Association), which used the rules of rugby except for a slight difference in the allocation of points.In 1887, Walter Camp introduced the skirmishes in the place of training (scrums) rugby. In 1892, it introduced a system downspara oppose the strategy of Princeton and Yale to control the ball without trying to achieve. In 1883 reduced the number of players at the request of Camp, to eleven, and Camp introduced the arrangement, which soon would become standard, seven-man offensive line with one quarterback, two halfbacks and a fullback.
In the 1890s, interlocking offensive formations like the flying wedge made the game extremely dangerous. Despite being implemented restrictions on flying wedge and other precautions, in 1905 eighteen players were killed in games. The presidenteTheodore Roosevelt informed the universities that the game would have to be made safer. However, it was not until 1910, after more deaths, the interlocking formations were banned.The pass was laid back in 1906. In 1912, the field has been placed in its dimensions above, the value of a touchdown was increased to 6 dots, and adding a fourth down.