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American football
A game consists of many individual plays. The vast
majority of these are scrimmage plays. Each play from scrimmage
is one of a series of downs given to the team with
possession. These two concepts, the concept of scrimmage, and the concept of
downs, are fundamental to American football, and are what distinguish it, as
well as
Canadian football, from most other forms of
football.
A set of downs begins with a first down,
which is given to a team either after it has just gained possession on the
previous play, or it has gained the necessary yardage from a previous set of
downs. On a first down, the team with possession is given four downs to gain
10 yards (they have "a first and ten", meaning that it is first down, and
they need ten yards to get another first down). The line a team must reach
in order to gain a first down is technically called the line to gain,
although it is commonly called first down yardage. The team
with possession is called the offensive team, and the other
team the defensive team.
Each down is a play from scrimmage. Prior to each play
from scrimmage, the two teams line up on opposite sides of a line of
scrimmage, which is defined by the spot of the ball from the
previous play. The spot is, in most cases, the yard line at which the ball
became dead on the previous play, plus or minus any penalty yardage. A down,
or play from scrimmage, begins with a snap and ends when
the ball becomes dead for any reason. A snap is either a handoff between the
legs from the center to the quarterback, or it is a pass between the legs
from the center to the quarterback, or possibly to a player other than the
quarterback, such as a punter or a holder for a field goal attempt. The ball
may become dead, ending the down, because a player in possession is tackled,
or because his forward progress is stopped, or because he goes out of
bounds, or because a forward pass goes incomplete.
There are two methods that can be used to advance the
ball while still maintaining possession:
- Running with the ball - The
quaterback, who is the player that normally has the ball following the
snap, may run the ball but, more often, he either hands the ball, or
throws a short pass to a running back, who then becomes the ball
carrier. Most other players on the offense have blocking
assignments.
- A
forward pass - A forward pass may only be thrown on a play
from scrimmage, and only from behind the line of scrimmage. It must be
thrown to an eligible receiver (any player who is not
an interior lineman). A completed pass is one caught by
an eligible receiver. The player may run with the ball after catching
it. An incomplete pass is any forward pass that either
hits the ground or goes out of bounds, at which point the ball becomes
dead, and is spotted at the preceding line of scrimmage for the
following play. An interception is a pass caught by the
defense, which transfers possession to the defending team, which may
then run with the ball.
If a team uses all four of its downs without gaining the
yardage for a first down, possession goes to the other team. Fourth down
situations are therefore pivotal. The offense has three choices: "go for
it", punt, or attempt a field goal.
Things the offense may decide to do on fourth down:
- "go for it" - If the distance
required for a first-down is short, a team may elect to go for it on
fourth down, but it is often risky. The safe thing to do is usually to
kick the ball.
- punt - A team will punt in order
to gain better field position.
- attempt a field goal - Field
goal attempts must be made with the ball on the ground (they cannot be
punted), so a player called a holder holds the ball for
a kicker. (In times past, a kicker may try a "drop
kick" -- that is, drop the ball and kick it after it bounces off the
ground -- and if the kicker kicks it through the goalposts, it is a
field goal. This is difficult to do, as the ball is in the shape of a
prolate spheroid and the bounce is unpredictable. Nowadays, the only
time you will see this is by a hurried kicker after a broken play.)
Failed field goal attempts, if they are short, can be returned by the
opponent, but the ball usually goes past the end line and can't be
returned. If the field goal attempt fails, the ball is spotted at the
original line of scrimmage, and possession is given to the other team.
(In the NFL, failed field goal attempts are spotted at the spot of the
kick.)
A team will occasionally run a trick play on fourth
down. They will line up as if to punt or attempt a field goal, but will
instead run the ball or pass it in an attempt to pick up a first down.
With its unlimited substitutions, American football is
highly specialized, with most teams having three specialized units: an
offensive unit, a defensive unit, and
special teams. There are many specialized players within
each units. Some players may only be used in certain situations. (for
details see:
offensive unit,
defensive unit,
special teams.)
Some of the more common penalties are listed below. In
most cases the offending team will be assessed a penalty of 5, 10 or 15
yards, depending on the infraction. There may also be a loss of down for a
penalty against the offense. A penalty against the defense may result in an
automatic first down. In some cases, the offense will be given the option of
declining the penalty and taking the yardage gained on the play. For some
infractions by the defense, the penalty is applied in addition to the
yardage gained on the play. A personal foul, which involves
danger to another player, usually results in a 15 yard penalty.
- Note: The neutral zone
is the space defined by lines drawn through the ends of the ball
parallel to the yard lines when the ball is spotted and ready for play.
No player may legally have any part of his body in the neutral when the
ball is snapped, with the exception of the center.
- False start (5 yards) - a
lineman moving before the snap in a way that similuates the start of the
play
- Illegal motion (5 yards) -
having more than one back in motion at the snap
- Illegal shift (5 yards) - not
being set before the snap
- Illegal formation (5 yards) -
having less than 7 players on the line of scrimmage
- Delay of game (5 yards) -
allowing too much time to elapse before the snap
- Inelligible receiver downfield
(5 yards) - a lineman beyond the neutral zone prior to a forward pass
- Illegal forward pass (5 yards
and loss of down) - thrown from beyond the neutral zone, or a second
forward pass on the same play.
- Holding (10 yards) - illegal use
of the hands or arms while blocking
- Offensive pass interference (10
yards) - interfering with a defender attempting to catch a pass
- Intentional grounding (10 yards
and loss of down) - throwing the ball into the ground to avoid being
tackled
- Clipping (15 yards) - an illegal
block from behind below the waist
- Illegal block (15 yards) -
usually a "crackback block".
- Offside (5 yards) - making
contact with an offensive lineman before the ball is snapped. or being
in the neutral zone when the ball is snapped. The offense can decline
the penalty and take the yardage gained on the play.
- Running into the kicker (5
yards) - during a kick from scrimmage
- Pass interference (automatic
first down no more than 15 yards from previous line of scrimmage)
- Piling on (15 yards)
- Roughing the kicker (15 yards) -
- Roughing the passer (15 yards) -
also called unnecessary roughness
- Too many players on the field (5
yards)
- Grabbing the face mask (5 or 15
yards) - if intentional, 15 yards; if unintentional, 5 yards. Just
touching an opponent's face mask, without grabbing it, is not illegal.
American football in its current form grew out of a
series of three games between
Harvard University and
McGill University of
Montreal in
1874. McGill played by the
Rugby Union code while Harvard played the
Boston Game[?], which was closer to
Association Football. As often happened in those days of far from
universal rules, the teams alternated rules so that both would have a fair
chance. The Harvard players liked having the opportunity to run with the
ball, and in
1875 persuaded
Yale University to adopt Rugby Union rules for their annual game. In
1876 Yale, Harvard,
Princeton, and
Columbia formed the
Intercollegiate Football Association[?], which used the Rugby Union
code, except for a slight differnce in scoring.
In 1880
Walter Camp introduced the scrimmage in place of the rugby
scrum. In 1882 the system of downs was introduced to thwart Princeton's
and Yale's strategy of controlling the ball without trying to score. In 1883
the number of players was reduced, at Camp's urging, to eleven, and Camp
introduced the soon standard arrangement of a seven-man offensive line with
a quarterback, two halfbacks, and a fullback.
By the 1890s interlocking offensive formations such as
the flying wedge had made the game extremely dangerous. Despite restrictions
on the flying wedge and other precautions, in 1905 eighteen players were
killed in games. President
Theodore Roosevelt informed the universities that the game must be made
safer. However, it was not until 1910, and after further deaths, that
interlocking formations were outlawed.
The forward pass was introduced in 1906. In 1912 the
field was changed to its current size, the value of a touchdown was
increased to 6 points, and a fourth down was added. The game had achieved
its modern form.
- NFL
History and the basics (http://ww2.nfl.com/basics/history_basics.html)
- NFL
Digest of Rules (http://ww2.nfl.com/fans/rules/index.html) -
(a basic guide)
- NCAA
Playing Rules (http://www.ncaa.org/library/rules.html)
(complete college football rules are available as a pdf file)
-
Guide to referee signals (http://www.nickstudio.com/~joe/nctfl/secondary_html/official_signals.htm)
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