When did zone defense begin in nba?

Zone defense began to gain traction in the NBA during the 1980s, although it had been used informally before then. The introduction of the 2-3 zone defense was notably popularized by the Detroit Pistons during their championship run in the late 1980s. However, it wasn't until the early 2000s, particularly with the emergence of the "zone" rules, that zone defenses became more formally recognized and utilized in the league.