The history and description of one of the most popular sports in USA.

3. American football resulted from
several major divergences from
rugby football, most notably the
rule changes instituted by Walter
Camp, considered the "Father of
American Football." Among these
important changes were the
introduction of the line of
scrimmage and of down-and-
distance rules.
Walter Camp

4.  The origin of professional football can be traced back to
1892, with William “Pudge” $500 contract to play in a game
for the Allegheny Athletic against the Pittsburgh Athletic Club.
 The first Professional "league" was the Ohio League, formed in
1903, and the first Professional Football championship game
was between the Buffalo Prospects and the Canton Bulldogs
in 1919.
 In 1920, the American Professional Football Association was
formed.
 The first game was played in Dayton, Ohio on October
3, 1920 with the host Triangles defeating the Columbus
Panhandles 14–0.
 The league changed its name to the National Football
League (NFL) two years later, and eventually became the
major league of American football.
 High school football dates to the 1880s and enjoys regional
popularity.

5. Football is played on a field 360 by 160 feet (109.7 by 48.8 meters).
The longer boundary lines are sidelines, while the shorter boundary
lines are end lines. Sidelines and end lines are out of bounds.

6. Near each end of the field is a goal line; they are 100 yards
(91.4 m) apart. A scoring area called an end zone extends 10
yards (9.1 m) beyond each goal line to each end line. The
end zone includes the goal line but not the end line. Yard
lines cross the field every 5 yards (4.6 m), and are numbered
every 10 yards from each goal line to the 50-yard line, or
midfield.

7. At the back of each end
zone are two goalposts
(also called uprights)
connected by a crossbar
10 feet (3.05 m) from the
ground. For high skill
levels, the posts are
18 feet 6 inches (5.64 m)
apart. For lower skill
levels, these are widened
to 23 feet 4 inches
(7.11 m).

8. Each team has 11 players on the field at a time. Usually there
are many more players off the field. Teams may substitute for
any or all of their players during the breaks between plays. As
a result, players have very specialized roles and are divided
into three separate units: the offense, the defense and the
special teams.

9.  The game begins with a coin
toss to determine which team
will kick off to begin the game
and which goal each team will
defend.
A standard football game
consists of four 15-minute
quarters with a half-time
intermission after the second
quarter. The clock is stopped
after certain plays, therefore, a
game can last considerably
longer.

10. The team that takes possession of the ball (the offense) has
four attempts, called downs, in which to advance the ball at
least 10 yards toward their opponent's (the defense's) end
zone.

11. The ball is always put into play by a snap. Offensive
players line up facing defensive players at the line
of scrimmage. One offensive player, the
center, then passes the ball backwards between
his legs to a teammate behind him, usually the
quarterback.

12. Players can advance the ball in two ways:
 By running with the ball, also known as rushing.
 By throwing the ball to a teammate, known as a
pass or as passing the football.

13. A down ends, and the ball becomes dead, after any of the
following:
 The player with the ball is forced to the ground (a tackle) or has
his forward progress halted by members of the other team (as
determined by an official).
 A forward pass flies beyond
the dimensions of the field
(out of bounds) or touches
the ground before it is
caught. This is known as an
incomplete pass.
 The ball or the player with
the ball goes out of bounds.
 A team scores.

14.  A touchdown (TD) is worth 6 points. It is scored when a player
runs the ball into or catches a pass in his opponent's end
zone.
 A field goal (FG) is worth 3 points, and it is scored by kicking
the ball through the goalposts def
 A safety, worth 2 points, is scored by the opposing team
when the team in possession at the end of a down is
responsible for the ball becoming dead behind its own goal
line. For instance, a safety is scored by the defense if an
offensive player is tackled, goes out of bounds, or fumbles the
ball out of bounds in his own end zone. ended by the
opposition.

15. In the United States, the major forms are
high school football, college football and
professional football.
The highest level major professional league
in the United States is the 32-team National
Football League (NFL).