Title: Defensive three-second violation
Content:  become legal, or if the defender is guarding a player who has possession of the ball. The team committing a defensive three-second violation is assessed a team technical foul. The offense receives one free throw and retains possession of the ball. The NBA also made zone defenses legal prior to the 2001–2002 season. However, the defensive three-second violation makes it difficult for NBA defenses to play zone, since zone defenses usually position a player in the middle of the key to stop penetration. The Philippine Basketball Association used to follow the illegal defense rule until the 2003 PBA season, when it was abolished. The WNBA adopted its own defensive three-second rule in 2013.
Title: Three seconds rule
Content:  The three seconds rule (also referred to as the three-second rule or three in the key, often termed a lane violation) requires that in basketball, a player shall not remain in their team's foul lane for more than three consecutive seconds while that player's team is in control of a live ball in the frontcourt and the game clock is running. The countdown starts when one foot enters the restricted area and resets when both feet leave the area. The three-second rule was introduced in 1936 and was expressed as such: no offensive player, with or without the ball, could remain in the key, for three seconds or more. The three-second rule came about in part following a game at Madison Square Garden 
Title: Technical foul
Content:  was designed to stop defenders from dropping back into a zone and thus preventing drives to the basket. The penalty, after a warning, was a technical foul charged to the offending team and one shot for the offense, except that if the first violation occurred within 24 seconds of the end of a period, the technical was assessed without warning. Beginning with the, the rule, now known as "Defensive Three Seconds," prohibits a defender from being in the shooting lane for three seconds, unless guarding an opponent within arm's reach (or the player with the ball, regardless of distance). 
Title: Leroy Edwards
Content:  Edwards is generally recognized as the player responsible for the implementation of the three-second rule. Enacted in 1936, it was originally designed to limit rough play near the basket. The rule limits the time players can remain in the area in front of the basket known as the "paint" or free-throw lane. The rule has been modified and is still used today.
Title: Defensive three-second violation
Content:  A defensive three-second violation, also known as illegal defense, is a basketball rules infraction in the National Basketball Association (NBA). It is assessed when a member of the defending team spends more than three seconds in the free throw lane (also called the key, the 16-foot lane, or "the paint") while not actively guarding an opponent. To be considered actively guarding an opponent, a defender must be within arm's length of an opponent and must be in a guarding position. A violation will not be called if an offensive player is in the act of shooting, if the offensive team loses control of the ball, if it is imminent that the defender's position 
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: Rules of basketball
Content:  The first time restriction on possession of the ball was introduced in 1933, where teams were required to advance the ball over the center line within ten seconds of gaining possession. This rule remained until 2000, when FIBA reduced the requirement to eight seconds, the NBA following suit in 2001. The NCAA retains the 10-second rule for men's play, and adopted this rule for women's play starting with the 2013–14 season. U.S. high schools, whose rules are drafted by NFHS, also use the 10-second rule for both sexes. In 1936 the three-second rule was introduced. This rule prohibits offensive players from remaining near their opponents' basket for longer than three seconds (the precise restricted area 
Title: Rules of basketball
Content:  by waiting close to the basket. When the NBA started to allow zone defense in 2001, a three-second rule for defensive players was also introduced. The shot clock was first introduced by the NBA in 1954, to increase the speed of play. Teams were then required to attempt a shot within 24 seconds of gaining possession, and the shot clock would be reset when the ball touched the basket's rim or the backboard, or the opponents gained possession. FIBA adopted a 30-second shot clock two years later, resetting the clock when a shot was attempted. Women's basketball adopted a 30-second clock in 1971. The NCAA adopted a 45-second shot clock for men while continuing 
Title: 1933–34 NCAA men's basketball season
Content: The "10-second" rule went into effect, requiring the team on offense to get the ball past the midcourt line within 10 seconds. ; A new substitution rule allowed each player to re-enter a game twice. Previously, each player could re-enter a game only once. ; The number of referees increased from one to two. 
Title: 1935–36 NCAA men's basketball season
Content:  A new rule prohibited any offensive player with the ball from standing in the free-throw lane (also known as the "key") for more than three seconds. Previously, this rule had applied only to a player who had possession of the ball.

Question: when was the defensive 3 second rule implemented?
Answer: the 2001–2002 season.
2001–2002 season.