Some football rules include the number of players on a team, the kickoff, the down system and the scoring system. The NFL's rule book spans more than 100 pages.
A football game begins with one team kicking off the football to the other team. After a team scores, the scoring team must kick off the ball to the other team. The football is also kicked off at the beginning of the second half. Generally, a coin toss before the game decides which team kicks off.
On a football team, only 11 players are allowed on the field during a play. One group of players is assigned to offense, which involves advancing the ball down the field. Another group of players is assigned to defense, which involves preventing the offense from scoring. Special teams play during kicks and punts.
Once the offense begins its possession, the team must advance the football at least 10 yards in four attempts, called downs. A football team can advance the ball by carrying it while running or throwing the ball to another offensive player. If the team fails to earn 10 yards, the other team's offense takes possession of the ball at the spot where last play ended. As a result, a common strategy is to punt the ball after three unsuccessful downs to improve the defense's field position.
A team can score three points by kicking the ball between the goal posts from any position on the field. A team scores six points when it scores a touchdown, advancing the ball into the opposing team's end zone. Other forms of scoring in football are extra points, two-point conversions and safeties.