Question: when did the nba start playing zone defense?
Answer: the 2001 -- 2002 season, 2002

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.