NFL

The league comprises 32 clubs, split into two conferences — the American Football Conference and the National Football Conference — of 16 clubs each. Each conference is divided into four divisions of four clubs, giving eight divisions in total.

Divisions matter more than they do in a sport that simply ranks everyone together. Because a club plays its division rivals twice each season, winning a division is a concrete route into the post-season regardless of how the club compares with the rest of its conference.

The regular season

Clubs play a set number of regular-season games determined by the league, and the arrangement of opponents is not a simple round-robin. Each club plays its division rivals twice, a rotating set of clubs from other divisions in its own conference, and a smaller set from the other conference. The league has changed the length of the regular season before, so the current figure is one to confirm with the NFL rather than assume from a previous season.

The post-season

The playoff field is 14 clubs. In each conference, the four division winners qualify, plus three additional clubs with the best remaining records — the wild cards. The field is then seeded, and the highest-seeded club receives a bye straight into the divisional round.

Every post-season round is single elimination: one game decides who advances. The two surviving clubs meet in the Super Bowl, played at a pre-selected neutral venue.

Seeding and tie-breakers

Seeding determines who hosts. Because hosting is a real competitive advantage, the tie-breakers that separate clubs with identical records are administratively important. They are applied in a defined order and include head-to-head results, record within the division and conference, record against common opponents, and strength-of-victory measures. The full list and its order sit in the NFL's own tie-breaking procedures, and the league revises them periodically — so a tie-breaker remembered from an earlier season may no longer be first in the sequence.

How the game is scored and progressed

The mechanics are durable, which is why they are safe to explain here without a date.

• Downs. The team in possession has four attempts — downs — to advance the ball ten yards. Achieving that distance resets the count to a new first down.
• Points. A touchdown is worth six, with the option of a one-point kick or a two-point conversion attempt afterwards. A field goal is worth three. A safety, where the defence tackles the ball carrier behind their own goal line, is worth two.
• Turnovers. Losing the ball through an interception or a fumble hands possession to the other team and is usually the single largest swing in a game.
• The clock. The game clock stops on incomplete passes, out-of-bounds plays and scores, which is what makes a late lead fragile and drives the use of timeouts and the two-minute warning.
• Review. Certain calls are reviewable, either by the officials or by a coach's challenge. Review rules and what is reviewable have been amended repeatedly.