Questions about the sport of basketball in general. For the American professional basketball league, see [nba].

Basketball is a team "ball and goal" sport in roughly the same class as hockey, lacrosse, association football etc, but differs from these in that it is a non-contact sport, and in the unique design of the goals. It was invented by James Naismith in 1891 as an activity for his gym class on a rainy day, originally using a soccer ball and two peach baskets, hence the name "basket-ball".

Modern basketball is played on a court 94' long by 50' wide (slightly smaller for high school, recreational or international play), with a hard, level floor surface such as wood or concrete, and two "baskets", each composed of a horizontal 18"-diameter hoop with attached fiber net, affixed to a vertical "backboard" and placed with the rim 10 feet above the floor and the backboard slightly inside the out-of-bounds lines, on opposing ends of the court. The primary equipment is the basketball itself, an inflatable, usually orange-brown rubber-composite ball about 30 inches in circumference. A game is played by two teams; formal basketball teams normally consist of ten players who "dress" for each game, five of which are on the court in active play at any one time. Casual recreational games can be played with any even number of players, from two (one-on-one) up to a dozen or more.

Players attempt to move the basketball across the court by bouncing it off the floor ("dribbling" it) while moving, and by throwing or "passing" the ball to their teammates. The rules prohibit moving with the ball without dribbling ("travelling"), and once a player has started dribbling and then stopped and taken the ball in both hands, or supported it from underneath, they may not begin dribbling the ball again (a "double dribble"). Once within range of the basket, players may throw or "shoot" the ball toward the basket with the idea of getting the ball to fall through the hoop and net from above. Doing so earns the scoring team two points for a shot made from close range, and three points if the shot was made from outside a roughly circular line with a radius approximately 20 feet from the basket (this differs slightly at various levels of play). In most formal leagues of play, a team has 24 seconds from the time the team gains possession in order to make a shot, before possession changes to the opposing team; this time is tracked on a "shot clock", first added to the game in 1954 to discourage teams simply playing "keep-away" after gaining a lead.

The team not in possession attempts to prevent the other team from making a basket, but no player (offensive or defensive) may make any "aggressive contact" with the opposing team's players, typically called a "personal foul" or just a "foul". They may typically only touch the ball with their hands or arms during a defensive move, such as intercepting a pass, "stealing" the ball from a dribbling player, blocking a shot or making a "rebound" (catching the ball after an unsuccessful shot). Almost any other contact made with hands, arms or shoulders on another player is a foul, and if the foul was made on a player attempting to shoot the ball, or if the team has committed a certain number of total fouls, a number of "free throws" are awarded to the player who was fouled. If a player accumulates five fouls before the end of the game, he is ejected from the game and his team must play without him.

In addition, "technical fouls" are called for egregious violations of the rules such as "flagrant fouls" (intentional, forceful personal fouls), intentional damage to the court or equipment, or poor sportsmanship including physical or verbal abuse of officials. A player who receives two technical fouls is ejected (often with additional penalties such as suspension from play in further games) and each technical foul results in the opposing team receiving two special free throws (made with no other player anywhere near the shooter).

However, in most leagues, "incidental body contact" between players is allowed, and players are entitled to be in their current position on the court at any time. This can often cause confusion to new players or spectators, as hard contact that can send a player to the locker room with a game-ending injury isn't penalized, but small restraining moves or what would appear to be unintentional contact between two players' arms is very often penalized.

In the United States, basketball is played professionally by all-male teams affiliated with the National Basketball Association or NBA, and all-female teams affiliated with the WNBA. Next to the NFL professional football league and Major League Baseball, NBA basketball is the third most popular spectator sport in the United States according to a recent ESPN survey, with collegiate-level NCAA basketball coming in fifth after collegiate football. It has international popularity as well, with many national teams and regional leagues outside the United States, and international play is governed by the French-based Federation Internationale de Basketball Amateur or FIBA (which as of 1989 no longer recognizes a distinction between amateur and professional players). Basketball is also an Olympic sport, with a tournament featured in every Games since 1936.