Title: Zone defense
Content:  specific player on the offense. A variant of this is triangle-and-two, in which three defenders are in a 2–1 zone and two defenders guard two specific offensive players. Zone defenses are common in international, college, and youth competition. In the National Basketball Association, zone defenses were prohibited until the 2001–2002 season, and most teams do not use them as a primary defensive strategy. The NBA has a defensive three-second violation rule, which makes it more difficult for teams to play zone, since such defenses usually position a player in the middle of the key to stop penetration. The Dallas Mavericks under coach Rick Carlisle are an example of an NBA team that have regularly used zone defenses.
Title: Man-to-man defense
Content:  Zone defenses were disallowed by the National Basketball Association in 1947. During this period, an illegal defense violation was called when a defender was either guarding an area instead of a specific offensive player or was double teaming an offensive player away from the ball. A rule change in 2001 eventually permitted zone defense but also specified that a defender who is standing inside the key is limited to not guarding an offensive player at arm's length for no more than three seconds. If the defender violates this rule, a technical foul is assessed against his team, and the opposing team is granted one free throw and subsequent possession of the basketball. This makes it difficult for NBA teams to play zone since such defenses usually position a player in the middle of the key to stop penetration. Man-to-man defense is still the primary defensive scheme in the NBA, and some coaches use it exclusively.
Title: Index of basketball-related articles
Content: Zone defense 
Title: 2–3 zone defense
Content:  In 1914, Eli Camden "Cam" Henderson's Bristol High School first used a 3–2 zone defense against Clair Bee's team, Grafton YMCA, in West Virginia. The zone defense was used because the gym floor was made of green pine and it was very slippery when wet, when the roof leaked. The 3-2 zone defense did not provide the rebounding support for the fast break that Cam Henderson was using. The top defender dropped back to form the 2–3 zone. Henderson developed this style of basketball successfully at Davis & Elkins College, before moving on to coach at Marshall University. In 1938, Marshall University upset Long Island University, to snap their 40-game winning streak. In 1947, Henderson led Marshall to a National Association of Intercollegiate Athletics (NAIA) championship title with his 2–3 zone defense and fast break offense. In 2003, Syracuse University coach Jim Boeheim led his team to an NCAA Tournament championship playing the 2–3 zone, which has become Boeheim's trademark.
Title: Zone defense
Content:  Frank Lindley, Newton, KS High School basketball coach from 1914 to 1945, was among the first to use the zone defense and other innovations in the game and authored numerous books about basketball. He finished his career with a record of 594–118 and guided the Railroaders to ten state titles and seven second-place finishes. Jim Boeheim, coach of the Syracuse Orange men's basketball team, is famous for using a 2–3 zone that is among the best in the NCAA. His zone, which typically features athletic, disruptive, and aggressive defenders, has become a prototype for use on other teams including the United States men's national basketball team, where he has spent time as an assistant coach.
Title: Zone defense
Content:  Zone defense is a type of defense, used in team sports, which is the alternative to man-to-man defense; instead of each player guarding a corresponding player on the other team, each defensive player is given an area (a zone) to cover. A zone defense can be used in many sports where defensive players guard players on the other team. Zone defenses and zone principles are commonly used in basketball, American football, association football, ice hockey, lacrosse, Australian rules football, netball and ultimate among others.
Title: 2–3 zone defense
Content:  The 2–3 zone defense is a defensive strategy used in basketball as an alternative to man-to-man defense. It is referred to as the 2–3 because of its formation on the court, which consists of two players at the front of the defense (closer to half court) and three players behind (closer to the team's basket).
Title: Zone blitz
Content:  Miami Dolphins defensive coach Bill Arnsparger developed the zone blitz in 1971. He started by placing linebackers on the defensive line and having them drop back into coverage, and eventually included regular defensive linemen as well. The scheme did not gain widespread use in professional football until Dick LeBeau refined it with the Cincinnati Bengals and popularized the zone blitz in the early '90s, while being the defensive coordinator for the Pittsburgh Steelers, earning Pittsburgh the title of "Blitzburgh". Though the zone blitz has become common throughout the NFL, the 3–4 defense—3 defensive linemen, 4 linebackers—lends itself particularly well to this style of play, and LeBeau has continued to utilize it as the defensive coordinator of the Tennessee Titans as recently as the 2017 season.
Title: Zone defense
Content:  The zone defence tactic, borrowed from basketball, was introduced into Australian football in the late 1980s by Robert Walls and revolutionized the game. It was used most effectively by Essendon Football Club coach Kevin Sheedy. The tactic is used from the fullback kick in after a behind is scored. The side in opposition to the player kicking in places their forward players, including their full-forward and centre half forward, in evenly spaced zones in the back 50-metre arc. This makes it easier for them to block leading players and forces the kick-in to be more precise, in effect increasing the margin for error which can cause a turnover and 
Title: College basketball
Content:  addition, the NBA limits what types of defense a team can play, primarily in an effort to prevent coaches from slowing down the pace of the game by using zone defenses. Zone defense is permitted in the NBA and WNBA; however, players cannot stand in the lane for more than three seconds if they are not guarding anyone. In NCAA basketball, no such restriction exists, and coaches are free to design a variety of defensive techniques. In college basketball, it is required by rule that the home team wears their white or light-colored jerseys while the visiting team wears their darker 

Question: when did the nba start playing zone defense?
Answer: 2002.
the 2001–2002 season.