A shot clock is a countdown timer used in a variety of games and sports, proving a set amount of time that a team may possess the object of play before attempting to score a goal. Shot clocks are used in basketball, water polo, lacrosse, poker and ringette. A shot clock is also used in snooker, college and pro lacrosse, water polo, korfball, and ten-pin bowling. It is analogous with the play clock used in American and Canadian football, and the pitch clock used in baseball. This article deals chiefly with the shot clock used in basketball.
The set amount of time for a shot clock in basketball is 24–35 seconds, depending on the league. This clock reveals how much time a team may possess the ball before attempting to score a field goal. It may be colloquially known as the 24-second clock, particularly in the NBA and other leagues where that is the duration of the shot clock. If the shot clock reaches zero before the team attempts a field goal, the team has committed a shot clock violation, which is penalized with a loss of possession.
At most professional and collegiate basketball courts the shot clock is displayed to the players and spectators in large red numerals below the game clock on a display mounted atop each backboard. In some collegiate and amateur facilities this display might be located on the floor or mounted to a wall behind the end line. A shot clock is used in conjunction with a game clock but is distinct from the game clock which displays the time remaining in the period of play.
The shot clock was originally introduced in the NBA in 1954 as a way to increase scoring and reduce stalling tactics that were commonly used before its inception. It has been credited with increasing fan interest in the then-fledgling league, and has since been adopted at most organized levels of basketball.
The shot clock is a digital clock that displays a number of seconds. The shot clock is usually displayed above the backboard behind each goal, allowing offensive players to see precisely how much time they have to shoot and officials to easily determine whether buzzer beaters should be counted. The NBA specifies that a transparent shot clock and game clock be part of the backboard assembly, and FIBA, EuroLeague, and many venues use this arrangement.
Three signals indicate when the time to shoot has expired:
In the final five seconds to shoot, the shot clock displays tenths of seconds. This was adopted in the 2011–12 NBA season, 2014–15 Euroleague, FIBA since 2018, and will be legalised in the NCAA starting in 2021.
The NBA has had a 24-second limit since 1954. FIBA introduced a 30-second shot clock in 1956 and switched to 24 seconds in 2000. The Women's National Basketball Association (WNBA) had a 30-second clock originally and switched to 24 seconds in 2006. Collegiate basketball uses a 30-second shot clock (details below).
The NBA had problems attracting fans (and positive media coverage) before the shot clock's inception.: 23–31 Teams in the lead were running out the clock, passing the ball incessantly. The trailing team could do nothing but commit fouls to recover possession following the free throw. Frequent low-scoring games with many fouls bored fans. The most extreme case occurred on November 22, 1950, when the Fort Wayne Pistons defeated the Minneapolis Lakers by a record-low score of 19–18, including 3–1 in the fourth quarter. The Pistons held the ball for minutes at a time without shooting (they attempted 13 shots for the game) to limit the impact of the Lakers' dominant George Mikan. It led the St. Paul Dispatch to write, "[The Pistons] gave pro basketball a great black eye.": 31–2 NBA President Maurice Podoloff said, "In our game, with the number of stars we have, we of necessity run up big scores.": 33 A few weeks after the Pistons/Lakers game, the Rochester Royals and Indianapolis Olympians played a six-overtime game with only one shot in each overtime: in each overtime period, the team that had the ball first held it for the entirety of the period before attempting a last-second shot. The NBA tried several rule changes in the early 1950s to speed up the game and reduce fouls before eventually adopting the shot clock.
In 1954 in Syracuse, New York, Syracuse Nationals (now the Philadelphia 76ers) owner Danny Biasone and general manager Leo Ferris experimented with a 24-second shot clock during a scrimmage. Jack Andrews, longtime basketball writer for The Syracuse Post-Standard, often recalled how Ferris would sit at Danny Biasone's Eastwood bowling alley, scribbling potential shot clock formulas onto a napkin. According to Biasone, "I looked at the box scores from the games I enjoyed, games where they didn't screw around and stall. I noticed each team took about 60 shots. That meant 120 shots per game. So I took 2,880 seconds (48 minutes) and divided that by 120 shots. The result was 24 seconds per shot.": 29 Ferris was singled out by business manager Bob Sexton at the 1954 team banquet for pushing the shot clock rule. Biasone and Ferris then convinced the NBA to adopt it for the 1954–55 season, a season in which the Nationals won the NBA Championship.
When it was introduced by the NBA, the 24-second shot clock made players so nervous that it hardly came into play, as players were taking fewer than 20 seconds to shoot. According to Syracuse star Dolph Schayes, "We thought we had to take quick shots – a pass and a shot was it – maybe 8–10 seconds... But as the game went on, we saw the inherent genius in Danny's 24 seconds – you could work the ball around [the offensive zone] for a good shot.": 29
The shot clock, together with some rule changes concerning fouls, revolutionized NBA basketball. In the last pre-clock season (1953–54), teams averaged 79 points per game; in the first year with the clock (1954–55), the average was 93 points, which went up to 107 points by its fourth year in use (1957–58).: 28 The advent of the shot clock (and the resulting increase in scoring) coincided with an increase in attendance, which increased 40% within a few years to an average of 4,800 per game.: 33–4
The shot clock received near-universal praise for its role in improving the style of play in the NBA. Coach and referee Charley Eckman said, "Danny Biasone saved the NBA with the 24-second rule." Boston Celtic all-star Bob Cousy said, "Before the new rule, the last quarter could be deadly. The team in front would hold the ball indefinitely, and the only way you could get it was by fouling somebody. In the meantime, nobody dared take a shot and the whole game slowed up. With the clock, we have constant action. I think it saved the NBA at that time. It allowed the game to breathe and progress." League president Maurice Podoloff called the adoption of the shot clock "the most important event in the NBA." The league itself states, "Biasone's invention rescue[d] the league."
Two later pro leagues that rivaled the NBA adopted a modified version of the shot clock. The American Basketball League used a 30-second shot clock for its two years in existence (1961–1963). The American Basketball Association also adopted a 30-second clock when it launched in 1967–68, switching to the NBA's 24-second length for its final season (1975–76).
From its inception in 1975, the Philippine Basketball Association adopted a 25-second shot clock. This was because the shot clocks then installed at the league's main venues, the Araneta Coliseum and Rizal Memorial Coliseum (the latter no longer used by the league), could only be set at 5-second intervals. The league later adopted a 24-second clock starting from the 1995 season. The Metropolitan Basketball Association in the Philippines used the 23-second clock from its maiden season in 1998. In Philippine college basketball, the NCAA Basketball Championship (Philippines) and the UAAP Basketball Championship adopted a 30-second clock, then switched to 24 seconds starting with the 2001–02 UAAP season 64, the first season to start after the FIBA rule change in 2001.
The shot clock begins counting down when a team establishes possession, and stops any time the game clock stops (e.g., timeouts, violations, fouls). The offensive team must attempt to score a field goal before the shot clock expires; otherwise, the team has committed a shot clock violation (also known as a 24-second violation in leagues with a 24-second shot clock) that results in a turnover to their opponents. An important distinction is that there is no violation if the ball is in flight to the basket when the shot clock expires, as long as the ball leaves the player's hand before the shot clock expires and the ball proceeds to go into the basket or touch the basket rim.
The shot clock resets to its full length at the start of each period and whenever possession changes to the opposite team such as after a basket is scored, the defense steals the ball or recovers a rebound, or the offense commits a foul or violation. The full length varies by country, level of play, and league; see the table below. The shot clock does not reset if a defender makes short contact with the ball (e.g., an attempted steal or a tipped pass) but the offense retains possession.
The shot clock also resets when the offense retains possession after a missed field goal or free throw (a missed field goal must touch the rim in order to reset the shot clock), or on certain fouls or violations that give the offense an inbounds pass in their frontcourt. However, in many of these cases where the offense does not have to travel the full length of the court, FIBA, NBA, WNBA, and other high-level leagues call for the shot clock to reset to a shorter length, most commonly 14 seconds (see below).
Near the end of each period, if the shot clock would ordinarily display more time than there is remaining in the period, the shot clock is switched off. During this time, a team cannot commit a shot clock violation.
The shot clock operator sits at the scorer's table. This is usually a different person from the scoreboard operator, as the task requires concentration during and after the shot attempt. In the 2016-17 NBA season, a new 'official timekeeper' deal for the NBA with Swiss watch manufacturer Tissot introduced technology to unify the keeping of the shot clock and the game clock. Tissot also became official timekeeper for the WNBA in the 2017 season.
If the offensive team is fouled and the penalty does not include free throws but just an in-bounds pass, the shot clock is reset. There are several cases where the offense is not given a full 24 seconds. The shot clock is instead set to 14 following an offensive rebound.: 7-IV-d FIBA adopted this in 2014 and the NBA adopted in 2018. The WNBA also observes this rule.
In several other cases where the offense inbounds the ball in its frontcourt (such as a foul by the defense not resulting in free throws), the offense is guaranteed 14 seconds.: 7-IV-e The shot clock is increased to 14 if it showed a shorter time.
On a held ball (whether decided by a jump ball or a possession arrow), the state of the shot clock depends on which team gets possession of the ball.
American collegiate basketball uses a 30-second shot clock, while Canadian university basketball uses a 24-second clock.
In men's collegiate basketball, there was initial resistance to the implementation of a shot clock for men's NCAA basketball, due to fears that smaller colleges would be unable to compete with powerhouses in a running game. However, after extreme results like an 11–6 Tennessee win over Temple in 1973, support for a men's shot clock began to build. The NCAA introduced a 45-second shot clock for the 1985-86 season; several conferences had experimented with it for the two seasons prior. It was reduced to 35 seconds in the 1993–94 season, and 30 seconds in the 2015–16 season. The NAIA also reduced the shot clock to 30 seconds starting in 2015–16.
Women's collegiate basketball (at the time sanctioned by the Commission on Intercollegiate Athletics for Women) used a 30-second shot clock on an experimental basis in the 1969–70 season, officially adopting it for the 1970–71 season.
The NCAA specifies 20 seconds rather than 30 after stoppages where the ball is already in the frontcourt. In 2019, it added offensive rebounds to this list.
The National Federation of State High School Associations (NFHS), which sets rules for high school basketball in the U.S., does not mandate the use of a shot clock, instead leaving the choice to use a clock and its duration up to each individual state association. While previous proposals for a national shot clock had been denied by the NFHS as recently as 2011, in the spring of 2021 the NFHS agreed to allow states the option of a 35-second shot clock, starting in 2022-2023. 
As of August 2021, 10 states either require a shot clock in high school competition or will begin using one starting in 2022-2023: California, Georgia, Iowa, Maryland, Massachusetts, New York, North Dakota, Rhode Island, South Dakota, and Washington. The District of Columbia also uses a 30-second shot clock for public school (DCIAA) competition, charter school competition (as of 2018-19), and for the DCSAA State Tournament, where public, private, and charter schools compete for the championship of the District of Columbia.
Kansas has expressly rejected use of a shot clock in high school on numerous occasions, a position which was reaffirmed in November 2021.
|NBA||24 seconds (but see 14-second clock above)|
|U Sports (Canadian universities)|
|NCAA, NAIA, USCAA, etc.||30 seconds|
|United States high school basketball||30/35 seconds (some states only)|
|FIBA||24 seconds (but see 14-second clock above)|
12 seconds (3x3 half-court)
|NCAA Men's||80 seconds|
|NCAA Women's||90 seconds|
|Ringette||International Ringette Federation (IRF)||30 seconds|
|Water polo||FINA||30 seconds|
|Canoe polo||ICF||60 seconds|
|Ten-pin bowling||PBA||25 seconds (only used on TV)|
|Snooker||Snooker Shoot Out||15 seconds (first five minutes)|
10 seconds (last five minutes)
(3 time-outs (40 sec.) possible)
|Poker||World Poker Tour||30 seconds|
99 seconds (optional)
A related rule to speed up play is that the offensive team has a limited time to advance the ball across the half-court line (the "time line").