The SLUBA Rules require all of the players in the league to be major leaguers under the age of 25. When the league was formed in 1984, most of the eligible players were born in the 1960s - thus the name.
SLUBA is named after legendary outfielder Sixto Lezcano who played mostly for Milwaukee. In 1993 Sixto was a hitting coach with the Eugene Emeralds of the Northwest League. Second League Commissioner for Life, Jack Fleming, sent letters to the Eugene team, to the Everett team, and to Sixto notifying them that the SLUBA Bosses would be in the stands (general admission) when Eugene first visited Everett (near Seattle). The SLUBA bosses made a pilgrimage to Everett and Sixto graciously allowed us to have a group photo taken and he autographed a baseball that is now the SLUBA Champion Traveling Trophy.