American football, known in the United States as football, is a team sport. It is played by two teams, eleven players to a side, who advance an oval ball over a rectangular field that is 120 yards long by 53.3 yards wide and has goalposts at both ends. The team in possession of the ball (the offense) attempts to advance down the field by running with or passing the ball. To continue their drive, the offense must advance the ball at least 10 yards down the field in a series of four downs.