American Football

American football is a gridiron code played between two teams of eleven, advancing an oval ball by running or passing it toward the opposing end zone; it is the dominant winter team sport in the United States. The offense has four attempts, called downs, to advance the ball ten yards; succeeding resets the count to a new first down, while failing turns the ball over to the opposing team. Scoring methods include the touchdown (six points, for advancing the ball into the opposing end zone, ordinarily followed by a one or two point conversion attempt), the field goal (three points, kicking the ball through the opposing goalposts) and the safety (two points, awarded to the defense for tackling a ball carrier in his own end zone). A standard game is four fifteen-minute quarters. The offense typically fields a quarterback, running backs, wide receivers, tight ends and an offensive line; the defense typically fields a defensive line, linebackers and defensive backs, though exact groupings vary considerably by scheme.