Football is a game in which two teams of eleven players compete to maneuver the ball into the opposing team’s end zone. The side scoring the most goals wins. The ball used in the game is round, covered with leather or some other material and inflated to 14.5-16 ounces (410-450 grams). There are four referees who officiate the game: the centre referee has sole authority, while two assistant referees officiate from the touchline and may advise him, particularly on issues of offsides and whether the ball has left the pitch. The fourth referee stands off the pitch in between both teams’ benches and controls substitutions.
During a normal game of football, each team gets four chances, or downs, to advance the ball 10 yards forward. The team that doesn’t make this progress in four downs loses possession of the ball to the defending team. This is known as a turnover on downs.
The offense moves the ball downfield by passing it to other members of their team. This involves the quarterback handing the ball off to one of their other players, called running backs or wide receivers, who attempt to gain as much ground as possible before they are tackled or forced out of bounds. The quarterback can also run with the ball, a tactic called “power running.”
On each play, the defense must attempt to stop the offense from making forward progress and prevent them from committing any penalties. Penalties are indicated by referees throwing yellow flags on the ground, and normally result in the offending team losing 5-15 yards of field position.
Special teams are responsible for the kicking aspect of the game, including place kick attempts that can score points and punts that return the ball to the other team after they fail to get a first down. A team can also decide to try for a point after a touchdown, which requires them to attempt a two-point conversion from a set distance behind their own goal line.
There are many different combinations of players that a coach can choose for his defensive unit. A “base” defense might consist of four defensive linemen, three linebackers and two cornerbacks, but coaches often change the composition of their teams to suit their style of play.