American football (known as football in the United States and gridiron in some other countries) is a sport played by two teams of eleven players on a rectangular field 120 yards long by 53.33 yards wide with goalposts at each end. The offense attempts to advance an oval ball (the football) down the field by running with or passing it. They must advance it at least ten yards in four downs to receive a new set of four downs and continue the drive; if not, they turn over the football to the opposing team.
Most points are scored by advancing the ball into the opposing team's end zone for a touchdown or kicking the ball through the opponent's goalposts for a field goal. The team with the most points at the end of a game wins. American football evolved in the United States, originating from the sport of rugby football. The first game of American football was played on November 6, 1869, between two college teams, Rutgers and Princeton, under rules resembling rugby and soccer. A set of rule changes drawn up from 1880 onward by Walter Camp, the "Father of American Football," established the snap, eleven-player teams and the concept of downs, and later rule changes legalized the forward pass, created the neutral zone, and specified the size and shape of the football. American football as a whole is the most popular sport in the United States; professional football and college football are the most popular forms of the game, with the other major levels being high school and youth football. As of 2012, nearly 1.1 million high school athletes and 70,000 college athletes play the sport in the United States annually. The National Football League, the most popular American football league, has the highest average attendance of any sports league in the world; its championship game, the Super Bowl, ranks among the most-watched club sporting events in the world, and the league has an annual revenue of around $10 billion.