Basketball

Two teams of five players score by putting the ball through the opponent's basket. A field goal inside the three-point arc is worth two points, beyond it three, and a free throw one. The team with more points when the game ends wins; a tie leads to an additional period.

The structural constraint that shapes everything is the shot clock: a team must attempt a shot within a set time or lose possession. Its length differs between rule sets — professional competitions commonly allow 24 seconds while some college rules allow longer — and that single figure changes how a game feels, from patient half-court play to fast transition.

Where rule sets diverge

• Length of a game. Games are divided into quarters, but the length of a quarter and therefore the total game time varies between competitions.
• Three-point distance. The arc sits at different distances in different competitions, and has been moved before. A shot that is worth three in one league may be a long two in another.
• Shot clock. Shorter clocks reward quick decision-making and increase possessions.
• Fouls and the bonus. The number of team fouls that triggers free throws, and how fouls are counted, differ between rule sets.
• Timeouts and reviews. Availability and mechanics vary considerably.

Because these differences are real, a comparison between teams or players from different competitions is rarely like-for-like. Points per game, for example, is affected by pace and game length before it says anything about a player.

The competitive landscape

Basketball is played at three broad levels, each with a different competitive logic.

• Professional domestic leagues. Each country or region runs its own league. Some, including the largest in North America, operate as closed leagues with no promotion or relegation, with entry to the next season decided by a post-season and squad building through a draft and trades. Others, particularly in Europe, use promotion and relegation between divisions and rely more on transfers and youth development.
• College competition. In the United States, universities compete within divisions and conferences, and the national champion is decided by a single-elimination tournament selected by committee rather than by league position. See the college sports hub.
• International competition. National teams compete under a single international rule set administered by the sport's world governing body, in continental championships, a world championship and the Olympic tournament. Clubs also compete internationally in continental competitions, with qualification usually earned through domestic league position.

International tournaments normally use a group stage followed by knockout rounds. Because the number of teams and the number of groups are set by the governing body and have changed over time, the current format is a figure to confirm.

How a domestic season is shaped

A typical professional season runs a regular season of scheduled games, weighted towards conference or divisional opponents, followed by a post-season. In closed leagues the post-season is a bracket of the best-record teams, sometimes with a preliminary round for those just outside the cut. In leagues with promotion and relegation, the league table decides the title and the bottom places decide who drops, often with an end-of-season play-off for the final promotion place.

Cups run alongside the league in many countries, using knockout ties. That is why a club can be eliminated from a cup midweek and continue its league campaign at the weekend.