Rules

1.1The field

The field is 100 yards long between the goal lines and 160 feet wide, with a 10-yard end zone at each end and goal posts on each end line. Yard lines cross the field every five yards.

1.2Protective equipment

Every player wears a helmet with a face mask, shoulder pads, leg protection and a mouth guard. A league's own rules say what else is compulsory.

2.1Eleven on the field

Each team has eleven players on the field. Substitutions are unlimited between plays.

2.2The offensive formation

At the snap the offence needs seven players on the line of scrimmage. Only the players on the two ends of the line and those in the backfield may catch a forward pass.

2.3Set and motion

Offensive players must be set for a full second before the snap. One back may then be in motion, as long as they are not moving toward the line.

3.1Quarters

A game is four quarters with a half-time break. The quarters are 15 minutes in the NFL and college and 12 in high school; leagues with shorter slots set their own.

3.2When the clock stops

The clock stops for an incomplete pass, a ball-carrier going out of bounds, a score, a change of possession, a penalty and a time-out. The offence has 40 seconds from the end of one play to snap the next.

3.3Overtime

Rule sets differ. The NFL plays an extra period in which each team gets a possession; college and high school give each team the ball in turn from a fixed yard line. Leagues may also let regular-season ties stand.

4.1Four downs for ten yards

A series is four downs in which the offence must reach the line to gain, ten yards ahead of where the series started. Reaching it earns a new series; failing gives the ball to the other team at that spot.

4.2The snap and the line of scrimmage

Each down starts with the centre snapping the ball. No player may be across the line of scrimmage when it is snapped.

4.3When the play is over

The ball is dead when the runner is down by contact, goes out of bounds or is stopped; when a forward pass is incomplete; or when a score is made.

4.4Fumbles

A ball that a player loses hold of is live, and either team may recover it and run with it.

5.1One forward pass

The offence may throw one forward pass a down, from behind the line of scrimmage. Backward passes are not limited.

5.2A catch

A pass is caught when a player in bounds controls the ball before it touches the ground and comes down in bounds. The NFL requires both feet in bounds; college and high school require one.

5.3Pass interference

Once a pass is in the air, a player may not push, hold or cut off an opponent to keep them from the ball. Interference by the defence gives the offence a first down, at the spot of the foul in the NFL and 15 yards on in college and high school.

5.4Intentional grounding

A passer under pressure may not throw the ball away to no receiver to avoid being tackled for a loss.

6.1Kick-offs

Each half, and play after every score, starts with a kick-off. The receiving team may run it back, or down it in its own end zone for a touchback.

6.2Punts

On fourth down the offence may punt the ball away to move the other team back.

6.3Fair catch

A returner who signals with an arm above the head may catch a kick without being hit, and may not then run with it.

7.1Points

A touchdown is 6 points, a field goal 3 and a safety 2. After a touchdown the scoring team tries for 1 point by kicking or 2 by running or passing the ball into the end zone.

7.2Touchdown

A touchdown is scored when the ball, in a player's possession, is on, above or behind the other team's goal line, or is caught in the end zone.

7.3Safety

A safety is scored when a team is downed with the ball, or fouls, behind its own goal line after putting the ball there itself.

8.1Before the snap

A false start by the offence, and encroachment or offside by the defence, cost five yards.

8.2Holding and illegal blocks

A blocker may not grab, hook or tackle an opponent. Offensive holding costs ten yards; a block in the back or below the waist in the open field is also a foul.

8.3Personal fouls

Hits on a defenceless player, hits with the crown of the helmet, grabbing the face mask, roughing the passer or the kicker, and late hits cost 15 yards, and the worst of them an ejection.

8.4How penalties are marked

The team fouled may accept the penalty, with the yards marked off and the down usually replayed, or decline it and take the result of the play.

8.5Unsportsmanlike conduct

Taunting, abusive language and fighting are 15-yard fouls, and two of them put a player out of the game.

9.1Standings

The rulebook decides a match; the league decides what a result is worth in its standings.

In this league: 3 points for a win, 1 point for a draw, 0 points for a loss.

9.2Teams level in the standings

The league also decides how teams level in the standings are separated.

In this league: Teams level on points are separated by most wins, then head-to-head, then point differential, then most points scored, then a coin flip recorded by the league. Head-to-head counts only when the tied teams have all played each other equally.

1.1The field

The field is 25 yards wide and 64 or 70 yards long including the end zones, with a midfield line that is the line to gain. Stepping on a boundary line is out of bounds.

1.2No-run zones

The five yards before midfield and the five yards before the goal line are no-run zones. A play that starts inside one must be a forward pass across the line of scrimmage.

1.3Equipment

Every player wears a flag belt with flags on the hips and a mouth guard. Shirts are tucked in, flags may not match the shorts, and jewellery, hats and exposed metal are not allowed.

2.1Starting the game

A coin toss gives the winner the choice of offence or defence and the loser the choice of direction. There are no kick-offs: the offence starts at its own 5-yard line.

2.2Downs

The offence has four downs to cross midfield, then three downs to score. If it fails, the other team takes over at its own 5-yard line, or at the spot of the ball if a team went for it on fourth down short of midfield.

2.3Punt or play

There is no kicked punt. On fourth down short of midfield the offence declares 'punt', which hands the ball over at the other team's 5-yard line, or 'play'.

2.4The clock

Games are two halves on a running clock that stops for half-time, injuries and time-outs. Each team has one time-out a half, and the offence has 40 seconds to snap once the ball is spotted.

2.5Mercy rule

In NFL FLAG regular-season play the game ends when a team leads by 35 points.

3.1Touchdown and extra point

A touchdown is 6 points. The scoring team then tries for 1 point from the 5-yard line, which must be a pass, or 2 points from the 10-yard line by run or pass.

3.2Safety

A safety is 2 points to the defence, scored when the ball-carrier is down in their own end zone.

3.3Interceptions

An intercepted pass may be run back. Returned for a score on a normal down it is 6 points; returned on an extra-point try it is 2.

4.1When the play is dead

The play ends when the ball-carrier's flag is pulled or falls out, they step out of bounds, a knee or arm touches the ground, the ball hits the ground, or a score is made. The ball is spotted where it was when the flag was pulled.

4.2No fumbles

A ball that hits the ground is dead where it landed, so there are no fumble recoveries.

4.3The quarterback cannot run

The player who takes the snap may not run the ball across the line of scrimmage. Hand-offs, pitches and laterals are allowed only behind the line, and whoever receives one may run or pass.

4.4Seven-second pass clock

The quarterback has seven seconds to throw. If they do not, the play is dead, the down counts and the ball goes back to the line of scrimmage. The clock no longer applies once the ball is handed off or pitched.

4.5One forward pass

One forward pass is allowed each play, thrown from behind the line of scrimmage and travelling beyond it. There is no intentional grounding.

4.6Who can catch

Every player is eligible to catch a pass. A receiver needs one foot in bounds with control of the ball.

4.7No diving or hurdling

A ball-carrier may not dive, jump or hurdle to gain ground; the ball is spotted where they left their feet. A player may dive to catch a pass or pull a flag.

5.1Rushing the passer

A defender who rushes the quarterback must start at least seven yards from the line of scrimmage when the ball is snapped. Once the ball is handed off or pitched, any defender may cross the line.

5.2Pulling flags

A defender stops the ball-carrier by pulling a flag, not by holding, pushing or tackling. A defender may not pull the flag of a player who does not have the ball.

6.1No blocking or contact

Blocking and screening are not allowed at any time, and team-mates near the ball-carrier must stop moving once the ball crosses the line of scrimmage. Deliberate contact by either side is a penalty.

6.2Flag guarding

A ball-carrier may not keep a defender from their flags by stiff-arming, dropping a hand, arm, shoulder or the head, or covering the flags with the ball or a shirt.

6.3How penalties are marked

Most penalties are five yards from the line of scrimmage: offensive fouls also cost the down, and defensive fouls give an automatic first down. Roughness and unsportsmanlike conduct are ten.