An evolution of rugby occurring in the United States. The game is, philosophically, an allegory of war in which two teams of eleven players each arrange themselves on each side of the line of scrimmage and proceed to beat the hell out of one another until one of a number of results is accomplished. Short-term intentions include, for the offense, the advancement of the football (colloquially known as a "pigskin"), and for the defense, the prevention of that advance.
The American football playing field is 120 yards (360 feet) long, with ten yards (30 feet) at each end of the field reserved as "end zones". The remaining hundred yards are demarcated every ten yards at least. Most football fields are marked every five yards (15 feet), and the hash marks mark each yard (3 feet).
The offense is given four downs in which it is expected to advance the ball at least ten yards. These ten-yard increments are referred to as first downs, and reset the series of downs. If a team fails to achieve a first down within the four allotted downs, the ball is given to the other team. This is called a turnover.
If the offense is able to advance the ball and carry it into the end zone, a touchdown is awarded, and six points are added to that team's score. The ball is then placed just outside the end zone, and the team is given a chance to score bonus points. If the ball is carried into the end zone, two points are added to the score. Typically, however, teams kick a PAT, or "point after touchdown".
The defense can score points as well. If a defender tackles an offensive player in the end zone behind the offense, two points are added to the defensive team's score. This is called a safety. More commonly, however, defensive players will intercept a forward pass and attempt to carry the ball to the end zone for a touchdown. If a defensive player intercepts the ball and does not score a touchdown, his team's offense will take the field. This is another form of a turnover. Yet another form of turnover comes when the offense fumbles the ball. A fumble occurs when an offensive player simply drops the ball. While the smartest thing to do is to simply fall down on the ball and end the play, many players elect to attempt to pick up the ball and run with it. A defensive player may pick up the ball and return it to the end zone.
Special teams refers to arrangements of players involved in the kicking of the football.
Typically, when the offense reaches fourth down, it will either punt or kick the football. A punt is a modified drop-kick in which the ball does not strike the ground before being kicked. Goalkeepers in soccer (international football) are known to kick the ball in this manner, as well, so the notion should not be unfamiliar to drunken fans of Manchester United and other assorted "soccer hooligans". The defense will attempt to catch the punt and return it for a touchdown. If the offense has moved close enough to the end zone, they may elect to kick a field goal, in which one player holds the ball upright on the ground while the kicker attempts to kick the ball through a goal post at the back of the end zone. A successful field goal is worth three points.
Blocked punts and field goals are considered fumbles, and can be returned for touchdowns or, failing that, a first down. A blocked PAT can be returned for a touchdown, but if the defense does not score a touchdown, the ball is given back to the offense, who is then obliged to a kickoff, which is exactly what it sounds like.
The War Game Philosophy
There is a famous quote from the American Revolutionary War that is variously attributed to General Israel Putnam or Col. William Prescott: "Don't shoot until you see the whites of their eyes". Some historians point out that the phrase originated some thirty-two years earlier with Lt. Col. Sir Andrew Agnew and the Scots Fusiliers at Dettingen. 
American football reflects a certain principle of warfare that held at least into the American Revolution by which two armies would line up, attack each other, collect themselves, and then repeat the process. The game is essentially a series of battles won by either the offense (touchdown, field goal) or the defense (punt, turnover, touchdown, safety). At the end of the game, a tally of the battle outcomes describes the winner according to the score.
• Acquitted murder suspect O.J. Simpson is a former American football superstar. He was the first running back to gain more than 2,000 yards in a single season.
• The championship game of the National Football League, the premier professional league, is called the Super Bowl.
• Super Bowl XLII, played at University of Phoenix Stadium in Arizona between the New York Giants and the New England Patriots on February 3, 2008, is now being seriously considered as the greatest football game ever played. It is certainly a leading candidate for the best Super Bowl ever. The Giants won 17-14, preventing the Patriots from achieving a perfect (unbeaten) season.