Locker was signed by the Sox in 1960, and pitched 2 seasons in the minors before missing the ’62 and ’63 seasons while in military service. He returned to the minors for the 1964 season. Although he was a starting pitcher in ’61 and ’64, he would never start again after 1964.
Bob made his major-league debut with the White Sox in April 1965. He was the #3 man in the bullpen during his rookie season, behind Eddie Fisher and Hoyt Wilhelm. It appears that the ChiSox mostly used just 8 pitchers that year. (Besides the 3 primary relievers, starters Tommy John and Bruce Howard made occasional relief appearances.)
Fisher was traded to the Orioles midway through the 1966 season, so Locker became the team’s closer, leading the team with 12 saves while compiling a 9-8 record and 2.46 ERA.
He was the bullpen ace again in 1967 (picking up 20 saves), as he and Wilhelm were joined by newly-acquired relievers Wilbur Wood and Don McMahon.
Wood became the team’s closer in 1968, but Locker and Wilhelm each pitched in 70 games, and all 3 reached double figures in saves.
Bob pitched in 22 innings over 17 games for the White Sox in early 1969, then in mid-June was traded to the Seattle Pilots for pitcher Gary Bell. Bob pitched in 51 games for Seattle that season.
In June 1970 the Brewers sold him to the Oakland Athletics. Bob pitched for Oakland through the end of the 1972 season as the #2 reliever behind Rollie Fingers. He appeared in the post-season in ’71 and ’72.
Locker was traded to the Cubs before the 1973 season and had a good year as the Cubs’ closer, picking up 18 saves and 10 wins. He was traded back to Oakland after the season, but missed all of 1974 after surgery for bone chips.
Bob returned to the Cubs for 1975, in exchange for outfielder Billy Williams. He pitched in 22 games and retired after the season.