Video "A Guide to american football"

Game Duration
A standard football game consists of four 15-minute (typically 12 minutes in high-school football) quarters, with a half-time intermission after the second quarter. The clock stops after certain plays; therefore, a game can last considerably longer (often more than three hours in real time).
If an NFL game is tied after four quarters, the teams play an additional period lasting up to 15 minutes. In an NFL overtime game, the first team that scores wins, even if the other team does not get a possession; this is referred to as sudden death. In a regular-season NFL game, if neither team scores in overtime, the game is a tie. In an NFL playoff game, additional overtime periods are played, as needed, to determine a winner.
Kick Off
Each half begins with a kickoff. Teams also kick off after scoring touchdowns and field goals. The ball is kicked using a kicking tee from the team's own 30-yard line in the NFL or from the 35-yard line in college football. The other team's kick returner tries to catch the ball and advance it as far as possible. Where he is stopped is the point where the offense will begin its drive, or series of offensive plays. If the kick returner catches the ball in his own end zone, he can either run with the ball, or elect for a touchback by kneeling in the end zone, in which case the receiving team then starts its offensive drive from its own 20-yard line. A touchback also occurs when the kick goes out-of-bounds in the end zone. A kickoff that goes out-of-bounds anywhere other than the end zone before being touched by the receiving team results in a penalty. Unlike with punts, once a kickoff goes 10 yards, it can be recovered by the kicking team. A team, especially one who is losing, can try to take advantage of this by attempting an Onside kick. Punts and turnovers in the end zone can also end in a touchback.After safeties, the team that gave up the 2 points puts the ball into play with a punt or placekick from its own 20-yard line.
10 yards
The team that takes possession of the ball (the offense) has four attempts, called downs, to advance the ball 10 yards towards their opponent's (the defense's) end zone. When the offense gains 10 yards, it gets a first down, which means the team has another set of four downs to gain yet another 10 yards or score with. If the offense fails to gain a first down (10 yards) after 4 downs, possession of the ball is given to the opposing team.
By running with the ball 'rushing'. One ball-carrier can hand the ball to another player or throw backwards to another player. These are known as as a handoff and a lateral respectively.
By throwing the ball to a teammate "forward pass". The offense can throw the ball forward only once on a play, only from behind the "line of scrimmage" and only before crossing the line of scrimmage. The ball can be thrown, pitched, handed-off, or tossed sideways or backwards at any time.
Rule violations are punished with penalties against the offending team. Most penalties result in moving the football towards the offending team's end zone. If the penalty would move the ball more than half the distance to the defense's end zone, the penalty becomes half the distance to the goal instead of its normal value.
Most penalties result in replaying the down. Some defensive penalties give the offense an automatic first down. Conversely, some offensive penalties result in the automatic loss of a down. If a penalty gives the offensive team enough yardage to gain a first down, they get a first down, as usual. If a penalty occurs during a play, an official throws a yellow flag near the spot of the foul. When the play ends, the team that did not commit the penalty has the option of accepting the penalty, or declining the penalty and accepting the result of the play.
Touch Down 6 points. It is scored when a player runs the ball or catches a pass in the opponent's end zone.
After a TD, the scoring team attempts a conversion. The ball is placed on the 2 yard line. If the ball is kicked over the crossbar and through the goal posts it's 1 point. If the team runs the ball or pass it into the End Zone it's 2 points.
A Field Goal worth 3 points, it is scored when the ball is kicked over the crossbar and through the goal posts.
For a safey it's 2 points. A safety is scored by the defense when the offensive player in possession of the ball is forced back into his own end zone and is tackled there or fumbles the ball out of his end zone.
Jersey's number
In the NFL, ranges of uniform numbers are reserved for certain positions:
1-9: Quarterbacks, kickers and punters
10-19: Quarterbacks, kickers, punters, and wide receivers
20-49: Running backs and defensive backs
50-59: Centers and linebackers
60-79: Offensive and defensive linemen
80-89: Wide receivers and tight ends
90-99: Defensive linemen and linebackers
American football is a collision sport. To stop the offense from advancing the ball, the defense must tackle the player with the ball by knocking him down. As such, defensive players must use some form of physical contact to bring the ball-carrier to the ground, within certain rules and guidelines. Tacklers cannot kick, punch or trip the runner. They also cannot grab the face mask of the runner's helmet or lead into a tackle with their own helmet. Despite these and other rules regarding unnecessary roughness, most other forms of tackling are legal. Blockers and defenders trying to evade them also have wide leeway in trying to force their opponents out of the way. Quarterbacks are regularly hit by defenders coming on full speed from outside the quarterback's field of vision.

To compensate for this, players must wear special protective equipment, such as a padded plastic helmet, shoulder pads, hip pads and knee pads. These protective pads were introduced decades ago and have improved ever since to help minimize lasting injury to players. An unintended consequence of all the safety equipment has resulted in increasing levels of violence in the game. Players may now hurl themselves at one another at high speeds without a significant chance of injury. Unfortunately, the injuries that do result tend to be severe and often season or career-ending and sometimes fatal. In previous years with less padding, tackling more closely resembled tackles in Rugby football, with less severe impacts and fewer injuries. Better helmets have allowed players to use their helmets as weapons. All this has caused the various leagues, especially the NFL, to implement a complicated series of penalties for various types of contact. Most recently, virtually any contact with the helmet of a defensive player on the quarterback, or any contact to the quarterback's head, is now a foul.

Despite protective equipment and rule changes to emphasize safety, injuries remain very common in football. It is increasingly rare, for example, for NFL quarterbacks or running backs (who take the most direct hits) to make it through an entire season without missing some time to injury.
Extra and optional equiptment such as neck rolls and knee pads help against injury as well, though they do not tend to be used by majority of players because of their lack of requirement.

The danger of football and the equipment required to reduce it make regulation football impractical for casual play. Flag football and touch football are less violent variants of the game popular among recreational players.

Both American football and soccer have their origins in varieties of football played in the United Kingdom in the mid-19th century. American football is directly descended from rugby football. The majority of the plays in a typical American football game involve handling the ball rather than kicking it.

Many "first" American football games have been claimed. However, many of the games offered as a "first" for American football were played under rules that were so different from today's game as to call into question the veracity of the claims. The origins of American football probably date to the early 1800s when teams from various colleges and secondary schools (necessarily from the Eastern part of the United States because established institutions of learning existed only in that region at the time) met to attempt to move an inflated ball past a line to gain points. This movement was usually achieved by kicking or batting at the ball, as in soccer. The number of men on each side (as men were only then allowed to compete) was quite different than the eleven which characterizes the modern game. As to the 'first' game of American football, it has been claimed that Rutgers University and Princeton University played the first game of college football on Nov. 6, 1869 in New Brunswick, New Jersey, won by Rutgers 6-4. However, the viewpoint that this particular game marks the beginning of American football is contested. The English Football (i.e., Soccer) Association rules were followed in the Princeton/Rutgers contest [8]; participants were only allowed to kick the ball; and each side had twenty five men. Some see the Princeton/Rutgers meeting of 1869 as the first intercollegiate game of "soccer" in America, but not American football [9]. Dartmouth College students played a football-like game now known as "Old Division Football," to which they published rules in 1871. If one must require that there be a starting point, or "first" game, of American football between two American teams, that distinction would have to go to the contest played between Tufts University and Harvard University on June 4, 1875 at Jarvis Field in Cambridge, Mass., won by Tufts 1-0 [7]. Jarvis Field was at the time located off Massachusetts Avenue in Cambridge, between Everett and Jarvis Sts. which bordered the northern point of the Harvard campus. A report of the outcome of this game appeared in the Boston Daily Globe of June 5, 1875. In the Tufts/Harvard game participants were allowed to pick up the ball and run with it, each side fielded eleven men, the ball carrier was stopped by knocking him down or "tackling" him, and the inflated ball was egg-shaped - the combination of which far more closely resembles the modern American football game than the games of other "firsts". Thus, the Harvard/Tufts game may be regarded as the beginning of football between two American colleges. It should also be noted that a year prior to the Tufts/Harvard game, Harvard faced McGill University of Montreal, Canada on May 14, 1874 in a game under rules similar to the Tufts/Harvard game. This marks the Harvard/McGill game as the first game of football in "North" America. To this day, Harvard, McGill and Tufts continue to field football teams though they no longer play each other.

One of the first egg shaped footballs.Encouraged by Yale University's Walter Camp, the schools began to adopt more standardized rules that would differentiate American football from rugby in the 1880s. The scrimmage was introduced in 1880 and the system of downs in 1882.

By the turn of the 20th century, football had become notoriously dangerous; 18 college players died in 1905 alone. Colleges responded with a series of rule changes to open up the game, most importantly the forward pass, along with outlawing dangerous formations such as the "flying wedge", and introducing and requiring better equipment such as helmets.

The game had achieved its modern form by 1912, when the field was changed to its current size, the value of a touchdown increased to 6 points, and a fourth down added to each possession. Originally dominated by the Ivy League, football soon captured the interest of colleges nationwide. By 1916, when the Rose Bowl game matching eastern and western teams became an annual event, football had developed a national following second only to baseball among team sports.

Professional football developed in the mill towns of Pennsylvania and the American Midwest in the early years of the 20th century. The NFL was founded in 1920 in Canton, Ohio as the American Professional Football Association; it adopted its current name in 1922. Professional football remained a largely regional sport of secondary importance until after World War II, when television broadcasts boosted NFL football's national appeal. The pro game surpassed both college football and baseball in popularity in the 1960s.[10] The first Super Bowl—between the champions of the NFL and the rival American Football League—was played in 1967, and the leagues merged in 1970.

Basic Strategy
Because the game stops after every down, giving teams a chance to call a new play, strategy plays a major role in football. Each team has a playbook of dozens to hundreds of plays. Ideally, each play is a scripted, strategically sound team-coordinated endeavor. Some plays are very safe; they are likely to get only a few yards. Other plays have the potential for long gains but at a greater risk of a loss of yardage or a turnover.
Generally speaking, rushing plays are less risky than passing plays. However, there are relatively safe passing plays and risky running plays. To deceive the other team, some passing plays are designed to resemble running plays and vice versa. There are many trick or gadget plays, such as when a team lines up as if it intends to punt and then tries to run or pass for a first down. Such high-risk plays are a great thrill to the fans when they work. However, they can spell disaster if the opposing team realizes the deception and acts accordingly.

The defense also plans plays in response to expectations of what the offense will do. For example, a "blitz" (using linebackers or defensive backs to charge the quarterback) is often attempted when the team on defense expects a pass. A blitz makes downfield passing more difficult but exposes the defense to big gains if the offensive line stems the rush.

Many hours of preparation and strategizing, including film review by both players and coaches, go into the days between football games. This, along with the demanding physicality of football (see below), is why teams typically play at most one game per week.