<P> When a team plays a zone, the defenders must keep their hands up and in passing lanes and quickly adjust their positions as the ball and the offensive players move around . Teams that successfully play zone defenses are very vocal and effectively communicate where they, the ball, and their opponents are or will be . </P> <P> Teams playing a zone occasionally try to "trap" the ball handler, an aggressive strategy of double - teaming the ball carrier . While this tactic may cause a turnover, it leaves one or more players on the offense undefended . The undefended player (s) are generally schemed to be on the opposite side of the court, away from the ball, so any attempt to pass the ball to them would result in long distance pass or a relay pass by a third offensive player, allowing the defense to recover . Good ball handlers can also try to "split" the trap by bringing the ball through the space in the middle of the two trapping defenders, creating an instant advantage for the offense . </P> <P> Zone defenses were prohibited in the National Basketball Association prior to the 2001--2002 season . The NBA now permits the use of zones, though most teams don't use them as a primary defensive strategy, and defenses featuring an unguarded defender inside the free throw lane are now disallowed (a violation that results in a defensive three - second violation, which is a technical foul that was also implemented in the 2001--2002 season). The Dallas Mavericks are an example of an NBA team that regularly uses zone defenses . During the 2011 Playoffs, their zone defense was credited with slowing down offenses, forcing opposing players to determine which defense they were playing . Zone defenses are more common in international, college, and youth competition because the defensive three - second violation 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 . </P> <P> Some of the reasons for using a zone defense are: </P>

When did zone defense start in the nba