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7.1 Fourth down situations
If a team uses all four of its downs without gaining the yardage for a first down or a touchdown, 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" - despite the risk involved, a team may always elect to "go for it" on fourth down by making one last all-out attempt to reach the first down marker, mounting a regular running or passing play to get there (just as they did on the first three downs). This is most common when, thanks to a team's success on the first three downs, the distance required for a first down is short; or when it is trailing late in the game by more than three points (the value of a field goal). The risk is significant: failing to make the next first down gives the ball to the opposing team with what is probably much better field position than a kick would leave them with. 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 might have tried a "drop kick" -- that is, dropping the ball and kicking 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 its 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 or the 20-yard line of the non-kicking team, whichever is farther from the goal line, and possession is given to the other team. (In the NFL, failed field goal attempts are spotted at the spot of the kick or the 20, whichever is farther from the goal line.) Field goals can also be attempted on other downs, but this is only seen in situations where a field goal will either win or tie the game and the distance to kick the field goal is well within range of the kicker.
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.
8 Specialized units and players
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, linemen.)
A list of player types and definitions can also be found in the Glossary of American football.
9 Penalties
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. Most of a number of personal fouls, which involve danger to another player, carry 15-yard penalties; in rare cases, they result in specific players being ejected from the game.
With three exceptions, no penalty may move the ball more than half the distance toward the penalized team's goal line. These exceptions are defensive pass interference (see the discussion of that penalty for more details), intentional grounding, and offensive holding - but in this last case the exception pertains only if the infraction occurs within the offensive team's own end zone, in which case an automatic safety is assessed (intentional grounding from the end zone also carries an automatic safety).
- 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 zone when the ball is snapped, with the exception of the center.
9.1 Penalties against the offense
- False start (5 yards) - any player moving after they have gotten in their set position before the snap in a way that simulates the start of the play (on occasion this is informally referred to as "traveling," because the signal the official makes to identify the penalty is almost exactly the same as the one a basketball referee makes when calling the infraction of traveling, or "walking" with the ball, in that sport)
- Illegal motion (5 yards) - having more than one back in motion at the snap, or a man in motion moving forward at the time of the snap
- Illegal shift (5 yards) - not being set before the snap
- Illegal formation (5 yards) - having fewer than 7 players on the line of scrimmage
- Delay of game (5 yards) - allowing the 40 seconds given to elapse before the snap (this is sometimes intentionally done on a play where the offense is about to punt from relatively advanced field position - and often the defensive team declines the penalty)
- Ineligible receiver downfield (5 yards) - a lineman beyond the neutral zone prior to a forward pass
- This penalty is not imposed if the receiver is behind the line of scrimmage when he receives the pass. This exception has been added to accommodate the screen pass, where a receiver (most often a back, but sometimes a tight end or wide receiver) catches a ball behind the line of scrimmage behind a "screen" of offensive linemen.
- Illegal forward pass (5 yards and loss of down) - thrown from beyond the neutral zone, or a second forward pass on the same play (originally, intentional grounding - see below - was considered a subset of this; they are now treated as separate infractions)
- Holding (10 yards) - illegal use of the hands or arms while blocking; an automatic safety is assessed instead if spot of infraction is within the offensive team's own end zone.
- Offensive pass interference (10 yards) - interfering with a defender attempting to catch a pass
- Intentional grounding - throwing the ball into the ground to avoid being tackled
- NFL penalty: 10 yards or spot of foul, whichever is farther from the original line of scrimmage, and loss of down
- College penalty: Spot of foul and loss of down
- In both NFL and college, intentional grounding from the offensive team's own end zone constitutes an automatic safety unless the defense chooses to decline the penalty, which might only ever happen if the infraction had occurred on a fourth-down play.
- Note that at any level, if the quarterback has moved outside the area between his offensive tackles, there is no penalty for grounding the ball if the quarterback throws the ball past the line of scrimmage. Also, "spiking" the ball into the ground to stop the clock is always legal, as long as the quarterback's primary intention is to stop the clock (or, far less commonly, to prevent the opposing team from making an instant replay challenge concerning the result of the immediately previous play, as no such challenge can be recognized once another play has been run).
- Illegal block in the back (10 yards) - an illegal block from behind and above the waist
- Clipping (15 yards) - an illegal block from behind and below the waist
- Illegal block (15 yards) - usually a "crackback block".
