American football and rugby: the main rule differences

Each team has 11 players on the field. Offensive, defensive and kicking specialists can take different roles; legal formations and receiver eligibility also matter.

Standard rugby union has 15 players per team. Forwards and backs have different roles, while specialist front-row requirements apply to contested scrums.

Regulation time is 60 minutes, split into four 15-minute periods. The game clock stops in specified situations; separate overtime rules may extend the game.

A standard match lasts 80 minutes, in two halves of no more than 40 minutes plus lost time. The half can continue until the ball next becomes dead, subject to exceptions.

The offense normally has four downs to gain 10 yards and earn a new series. Failure normally gives possession to the opponent; penalties can alter the series.

There is no fixed number of phases or required distance. Possession can continue through tackles, rucks and mauls while players comply with the laws.

One forward pass is permitted per down from behind the line of scrimmage, before the ball crosses it. Receiver-eligibility rules apply; backward passes are also possible. The forward pass must also precede any change of possession.

Players may pass sideways or backwards, but may not throw the ball forwards. A forward throw or knock-forward usually leads to a scrum, subject to the applicable exceptions.

A touchdown scores 6, a field goal 3 and a safety 2. A post-touchdown try scores 1 by kick or safety, or 2 by touchdown.

A try scores 5, conversion 2, penalty goal 3 and dropped goal 3. A penalty try awards 7 points without a conversion attempt.

A runner with possession can score when the ball reaches the goal-line plane under the touchdown rules. Touching the ball to the ground is unnecessary; catches must still be completed.

A try normally requires legally grounding the ball in the opponents’ in-goal, including on the try line. Merely carrying it across the line does not score.

A runner down by contact or stopped in forward progress normally ends the down. An untouched fall alone need not end it; live fumbles have separate recovery rules.

A tackle does not automatically end play. The tackler must release; the tackled player must make the ball available, and eligible players may contest possession legally.

Legal blocking can protect a runner or passer, but holding, illegal blocks and other prohibited contact are fouls. Scrimmage alignment and neutral-zone restrictions govern the start of plays.

Obstructing an opponent to shield the ball carrier is prohibited. Offside depends on the phase and player position; participation requires compliance with the relevant onside conditions.

Kickoffs, punts and field-goal attempts have distinct procedures. A fair-catch signal restricts advancement and protects the receiver; kick recovery rights depend on the type and circumstances.

Kicking in open play is allowed subject to offside. Restarts include drop-kicks, scrums and lineouts; the restart depends on why play stopped and where the ball went.

Required equipment includes an approved helmet, shoulder pads and other specified protective pads. Wearing protection does not permit dangerous contact prohibited by the player-conduct rules.

Permitted protection includes compliant soft headgear and padding. Hard protective equipment that fails the clothing requirements is prohibited; all clothing must comply with safety standards.

Any number of substitutes may enter while the ball is dead, subject to procedures. Repeated changes are possible; defensive matching after offensive substitutions normally applies before the two-minute warning.

Replacement numbers are limited, with up to 8 nominated replacements in internationals. Tactical replacements generally cannot return except in specified cases; temporary medical replacements have separate conditions.

Fouls commonly produce yardage penalties, sometimes loss of down or an automatic first down. Enforcement varies by foul and play; serious misconduct can lead to disqualification.

Sanctions include scrums, free-kicks and penalties; yellow cards suspend a player for 10 minutes. Red cards dismiss the player, with a limited 20-minute replacement rule in specified elite matches.