The Trent Tucker Rule is a basketball rule that disallows any regular shot to be taken on the court if the ball is put into play with under 0.3 seconds left in game or shot clock. The rule was adopted in the 1990–91 season and named after New York Knicks player Trent Tucker, and officially adopted in FIBA play starting in 2010. When the WNBA was established in 1997, this rule was adopted too.
- NOT UNDER 0.3 must expire on the game clock and shot clock when a ball is thrown inbounds and then hit instantly out-of-bounds. If under 0.3 expires in such a situation, the timer will be instructed to deduct AT LEAST 0.3 from the game clock and shot clock. If, in the judgment of the official, the play took longer than 0.3, he will instruct the timer to deduct more time. If under 0.3 remain on the game clock when this situation occurs, the period is over. If under 0.3 remain on the shot clock when this situation occurs, a shot clock violation is called.
- The game clock and shot clock must show at least .3 in order for a player to secure possession of the ball on a rebound or throw-in to attempt a field goal. Instant replay shall be utilized if the basket is successful on this type of play and the game clock runs to 0.0 or the shot clock expires on a made basket and the officials are not reasonably certain that the ball was released prior to the expiration of the shot clock. The only type of field goal which may be scored if the game clock and shot clock are at 0.2 or 0.1 is a “tip-in” or “high lob.”
The Article 16.2.5 of the 2010 FIBA Official Rules states: "The game clock must indicate 0.3 (three tenths of a second) or more for a player to gain control of the ball on a throw-in or on a rebound after the last or only free throw in order to attempt a shot for a field goal. If the game clock indicates 0.2 or 0.1 the only type of a valid field goal made is by tapping or directly dunking the ball."
The rule was born out of a game between the Knicks and the Chicago Bulls on January 15, 1990 at Madison Square Garden. The game was tied at 106 with one-tenth of a second left in regulation and the Knicks in possession. During a time-out called by the Knicks, both teams prepared for what was seen as the only possible way the Knicks could win in regulation: an alley oop tap-in from out of bounds by Patrick Ewing.
When play resumed, the Knicks player throwing the ball in, Mark Jackson, saw the alley-oop play get broken up. He proceeded to throw the ball inbounds to Tucker, who was the only player open. Tucker then turned around and hit a three-point jump shot before the buzzer, giving the Knicks the win, 109–106. Replays showed that the clock was not started until Tucker's shot was already midair and coming down towards the basket.
The Bulls, led by first-year head coach Phil Jackson, later filed an official protest with the NBA about the play. By their estimate, the play took closer to 0.4 seconds. However, timekeeper Bob Billings and referee Ronnie Nunn, who were working that game, claimed everything went perfectly fine. The protest was disallowed.
Vice president of operations Rod Thorn was the only NBA executive to side with the Bulls. (Incidentally, Thorn was once the general manager of the Bulls.) Thorn argued that it was physically impossible for a player to receive an inbounds pass and release it for a shot in less than a tenth of a second. He pointed out that tests in European basketball leagues, which had counted down the final minute of a period in tenths of seconds for many years (the NBA had just adopted it for 1989–90), proved that a catch-and-shoot takes at least three-tenths of a second.
Although the Bulls lost the protest, the dispute became the backbone for the time requirements of the new rule. Teams with the possession of the ball with less than 00.3 left also have the option of trying a Hail Mary shot like the one that the Knicks were going to try before Tucker's shot, or to simply let the clock run to zero.
At the start of the 1989–90 season, the NBA had adopted a rule from FIBA making game clocks register tenths of seconds in the final minute of a period. Madison Square Garden, like the majority of NBA venues at the time, used an American Sign & Indicator scoreboard. During the first weeks of the season, it was evident the manufacturer's scoreboards would have frequent calibration flaws with tenths in the final minute. In some cases the clock would be very inconsistent in timing tenths, while in other cases after calibration, the clock would actually "freeze" at one-tenth of a second before 00.0 appeared. The firm would be purchased by Trans-Lux eventually, and many college arenas which had AS&I scoreboards did not modify their scoreboards to carry tenths, knowing of the problems, until at least their purchase by Trans-Lux. (The NCAA did not officially adopt tenths until 2001; middle & high schools adopted this around 1990.)
The notorious scoreboard problems of the AS&I units led to most new arenas switching to rivals White Way, Daktronics (which Madison Square Garden now uses), or in recent years, Canadian manufacturer OES.
The late NBA Commissioner David Stern made it a requirement that all NBA arenas have their official game clocks properly calibrated in the wake of the incident, resulting in scoreboard overhaul. The AS&I scoreboards' notorious problem with clock mismanagement would sometimes still be a problem at some venues where the clock would still "hold" at one-tenth of a second, before the horn sounded. This was after Bulls coach Phil Jackson noted that this clock incident was not the first in Madison Square Garden. As a player for the Knicks in the 1970s, he noted that the clock there tended to run slower when they were behind, but faster when they were ahead.
Further changes in 1991 were designed to eliminate the problem with the AS&I units with a new directive for 1991–92 to add shot clocks with duplicate game time. At that point most venues purchased new scoreboards from White Way, Fair-Play, or Daktronics because of the calibration consistency of the new units.
Very few NBA teams purchased the AS&I (or later, Trans-Lux) units when the new rule was adopted in 1991. The last NBA arena to use the manufacturer's unit was the Charlotte Coliseum (II), which installed a successor Trans-Lux unit for the 2001–02 season (the Hornets' last in Charlotte, but the arena closed after the 2004–05 season, the Bobcats' inaugural season, after its replacement, the Spectrum Center, opened (with a new Daktronics unit). By 2011, all NBA venues used either a Daktronics or OES system.
In 2002, the NBA instituted new rules regarding the end of period indicators. A LED light strip on the backboard and the scorer's table replaced the traditional electric red light behind the backboard, and a shot clock visible to all three viewable sides was mandated.
Venues using Daktronics units installed new four-sided shot clocks with red indicator lights on the sides of the shot time to further assist the electric light. By 2004, shot clocks were available with a perimeter light strip around the clock that also lit up when the clock read 00.0. Today, the see-through shot clock units from Daktronics and OES have implemented the light strips that surround the shot clock that are turned on upon the clock registering 0.0.
In recent years, timekeeping rules have changed with the implementation of a system where the blowing of an official's whistle stops the clock at the instant of the whistle, along with a rule change where the on-court official (not an official at the scorer's table) starts the clock by pressing a button attached to the official's belt.
On December 20, 2006, New York Knicks forward David Lee scored a game-winning basket with only 0.1 left on the clock. The shot counted because Lee deflected in the inbounds pass into the basket (just like what was foreseen by the Knicks and Bulls in their game years before). This was the first occurrence of a team winning an NBA game with 0.1 left since Trent Tucker, and coincidentally from the same team, the New York Knicks. Furthermore, this took place after the NBA adopted the Precision Time Systems unit, where officials, not the timer, start the clock. In 2004, FIBA adopted a rule where the system would be mandatory in international competitions. Michael Jordan, Charles Oakley and Patrick Ewing, all of whom participated in the original Trent Tucker game, were in attendance at the David Lee game in Madison Square Garden.
In 2010, FIBA instituted Article 16.2.5 to officially institute the Trent Tucker Rule in international basketball.
Another example of this rule being invoked occurred at the end of a game between the University of South Florida and Florida Gulf Coast University on December 17, 2013, when FGCU appeared to tie the game at 68 on a Chase Fieler shot off a full-court inbounds pass with 0.3 seconds remaining in double overtime. Replays showed that Fieler got the shot off before the 0.3 expired, but the equivalent NCAA rule (Rule 5, Section 18, Article 1) was invoked to waive the Fieler basket, giving USF the win. However, under the FIBA and NBA interpretation, the restrictions only apply to 0.2 or 0.1, as the ball was put in play at 0.3. 
The NBA in 2016 adopted a deal with Tissot, requiring all scoreboards and shot clocks be manufactured by the Swiss timekeeper. All NBA venues must use the identical Tissot unit during games for consistency reasons.