Dunking in college basketball was banned in the National College Athletic Association (NCAA) from 1967 to 1976. Many people attributed this ban to the dominance of the then college phenomenon Lew Alcindor (Kareem Abdul-Jabbar). The no-dunking rule at the time was even referred to as the "Lew Alcindor rule" in news media and by basketball players.

A dunk is seen as a type of basketball shot that is performed when a player jumps in the air, controls the ball above the horizontal plane of the rim, and scores by putting the ball directly through the basket with one or two hands. It is considered a type of field goal; if successful, it is worth two points. The basketball must go into the basket from above the rim!

Dunk shots were specifically declared illegal to "equalize" play between defensive and offensive players. When the players were around the basketball nets, this ban was especially important since it helped to decide how players could score points. By using the dunking maneuver (when it was not banned), it didn't give a defense an opportunity to block a shot and prevent points from being made.

With the ban in place, a violation of the ban cost the team at fault possession of the ball. Also no points were given to the team that caused the violation (points for dunk basketball shots were not added to a team's score).

More Info: en.wikipedia.org