Football is a team sport in which players try to score points by running or passing the ball to other teammates, or kicking it into a goal. It is played on a field, either natural or artificial, that measures 120 yards long and 160 feet wide. It is divided by longer boundary lines, called sidelines, and shorter ones, called end lines. Near each end of the field is a scoring area, called the end zone. There are also yard lines that cross the field every five yards, and two rows of numbers, called hash marks, which indicate where plays start and stop.
There are two teams of eleven players each, and a maximum of 20 players on the field at one time. During the game, teams alternate playing offense and defense. The defending team must prevent the offensive team from scoring a touchdown or field goal by tackling, throwing down, or pushing the ballcarrier out of bounds. Unlike soccer, which originated in England, modern football is not played on a grass surface and forward passing is allowed.
The first play of the game is a kickoff. A player from the kicking team kicks the ball across the field to another team member, who must have both feet on or behind the end line. The receiving team then tries to run with the ball and pass it to other players. If a player on the kicking team touches the ball, it becomes dead and the officials must restart the game with a kickoff.
After the official puts the ball down on the field, an imaginary line called the line of scrimmage separates the two teams. On every offensive play, at least seven players must line up behind this line. The most important offensive players are the center, guards, and quarterback. A quarterback (QB) is the leader of the offense and is responsible for throwing, catching, and blocking. He is assisted by a tight end and wide receivers, who may specialize in catching or blocking.
A touchdown is worth six points. Besides a touchdown, a team can earn extra points by kicking the ball through the goal posts. A field goal is worth three points and can be placekicked or drop-kicked. A safety is worth two points and is scored by the defending team when it tackles a ball-carrier in his own end zone.
The defense tries to prevent the other team from scoring by tackling any player who has the ball or breaking up passes between the quarterback and receivers. Defensive backs, or safeties, line up behind the defensive line and cover the opponent’s receivers. They also rush the quarterback. If the quarterback throws an interception, the defensive backs return it to his own end zone for a touchdown. Other defensive responsibilities include preventing the other team from crossing the end zone.