🏈アメリカンフットボールのルール

American football is a collective contact sport played 11 against 11 on a 100-yard field bordered by two end zones. Two teams alternate between offense and defense to move an oval ball toward the opponent's zone. It is a strategic game broken into distinct plays, where every yard gained matters.

Score more points than the opponent by carrying the ball into their end zone or kicking it between the goalposts. The offense tries to advance, while the defense tries to stop it and regain possession.

• •The offense has 4 attempts ("downs") to gain at least 10 yards; succeeding earns a fresh set of 4 downs.
• •If the 10 yards are not gained in 4 downs, the ball is turned over to the opponent at that spot.
• •Every play starts with a "snap": the center hands the ball back to the quarterback.
• •The ball is advanced by running (a rush) or by throwing it forward (a pass); only one forward pass is allowed per play.
• •A player is stopped ("tackled") when a knee or body touches the ground under contact, or when they go out of bounds.
• •On 4th down, teams often punt or attempt a field goal rather than risk losing the ball.

A touchdown is worth 6 points and earns a try (1 point by kick, or 2 points by replaying from short range). A field goal kicked between the posts is worth 3 points. A safety (an offensive player downed in their own end zone) gives the defense 2 points. The running total determines each team's score.

A game is played over 4 quarters. Their length varies by federation: 15 minutes in the NFL and NCAA, generally 12 minutes in IFAF/youth play. A halftime break separates the 2nd and 3rd quarters; if tied, overtime rules specific to each federation apply.

The team with the most points at the end of regulation wins. If tied, an overtime period decides the game according to the federation's format (sudden death or alternating possessions).