Measurements and time limits discussed in this section often vary among tournaments and organizations; international and NBA rules are used in this section.
The object of the game is to outscore one's opponents by throwing the ball through the opponents' basket from above while preventing the opponents from doing so on their own. An attempt to score in this way is called a shot. A successful shot is worth two points, or three points if it is taken from beyond the three-point arc which is 6.25 meters (20 ft 6 in) from the basket in international games and 23 ft 9 in (7.24 m) in NBA games.
Playing regulations
Games are played in four quarters of 10 (international) or 12 minutes (NBA). College games use two 20 minute halves while most high school games use eight minute quarters. Fifteen minutes are allowed for a half-time break, and two minutes are allowed at the other breaks. Overtime periods are five minutes long. Teams exchange baskets for the second half. The time allowed is actual playing time; the clock is stopped while the play is not active. Therefore, games generally take much longer to complete than the allotted game time, typically about two hours.
Five players from each team (out of a twelve player roster) may be on the court at one time. Substitutions are unlimited but can only be done when play is stopped. Teams also have a coach, who oversees the development and strategies of the team, and other team personnel such as assistant coaches, managers, statisticians, doctors and trainers.
For both men's and women's teams, a standard uniform consists of a pair of shorts and a jersey with a clearly visible number, unique within the team, printed on both the front and back. Players wear high-top sneakers that provide extra ankle support. Typically, team names, players' names and, outside of North America, sponsors are printed on the uniforms.
A limited number of time-outs, clock stoppages requested by a coach for a short meeting with the players, are allowed. They generally last no longer than one minute unless, for televised games, a commercial break is needed.
The game is controlled by the officials consisting of the referee ("crew chief" in men's college and the NBA), one or two umpires ("referees" in men's college and the NBA) and the table officials. For college, the NBA, and many high schools, there are a total of three referees on the court. The table officials are responsible for keeping track of each teams scoring, timekeeping, individual and team fouls, player substitutions, team possession arrow, and the shot clock.
Equipment
The only essential equipment in basketball is the basketball and the court: a flat, rectangular surface with baskets at opposite ends. Competitive levels require the use of more equipment such as clocks, scoresheets, scoreboard(s), alternating possession arrows, and whistle-operated stop-clock systems.
A regulation basketball court in international games is 28 by 15 meters (approx. 92 by 49 ft) and in the NBA is 94 by 50 feet (29 by 15 m). Most courts are made of wood. A steel basket with net and backboard hang over each end of the court. At almost all levels of competition, the top of the rim is exactly 10 feet (3.05 m) above the court and 4 feet (1.2 m) inside the baseline. While variation is possible in the dimensions of the court and backboard, it is considered important for the basket to be of the correct height; a rim that is off by but a few inches can have an adverse effect on shooting.
There are also regulations on the size a basketball should be. If women are playing, the official basketball size is 28.5" in circumference (size 6) and a weight of 20 oz. For men, the official ball is 29.5" in circumference (size 7) and weighs 22 oz.
Violations
The ball may be advanced toward the basket by being shot, passed between players, thrown, tapped, rolled or dribbled (bouncing the ball while running).
The ball must stay within the court; the last team to touch the ball before it travels out of bounds forfeits possession. The ball-handler may not move both feet without dribbling, known as traveling, nor may he dribble with both hands or catch the ball in between dribbles, a violation called double dribbling. A player's hand cannot be under the ball while dribbling; doing so is known as carrying the ball. A team, once having established ball control in the front half of the court, may not return the ball to the backcourt. The ball may not be kicked nor struck with the fist. A violation of these rules results in loss of possession, or, if committed by the defense, a reset of the shot clock.
There are limits imposed on the time taken before progressing the ball past halfway (8 seconds in international and NBA; 10 seconds in NCAA and high school), before attempting a shot (24 seconds in the NBA, 30 seconds in NCAA women's and Canadian Interuniversity Sport play for both sexes, and 35 seconds in NCAA men's play), holding the ball while closely guarded (5 seconds), and remaining in the restricted area (the lane, or "key") (3 seconds). These rules are designed to promote more offense.
No player may interfere with the basket or ball on its downward flight to the basket, or while it is on the rim (or, in the NBA, while it is directly above the basket), a violation known as goaltending. If a defensive player goaltends, the attempted shot is considered to have been successful. If a teammate of the shooter goaltends, the basket is cancelled and play continues with the defensive team being given possession.
