Though he never made it to Major League Baseball as a player, he was a coach at the MLB level for the Seattle Pilots, Cincinnati Reds[1] and Oakland Athletics.

[3] Plaza shifted to second base with the Rochester Red Wings in 1956, and batted .297 with five home runs and 30 RBI in 121 games during his first season in Triple-A.

[3] He wrapped up an eleven-year playing career (all in the St. Louis Cardinals organization) in 1962 with the Atlanta Crackers, and immediately moved into coaching.

Pilots General Manager Marvin Milkes let Plaza go along with the rest of the coaching staff as the team struggled with bankruptcy and a host of other issues after completing their one and only season in Major League Baseball.

Plaza coached in the Cincinnati Reds' farm system following his stint in Seattle, and joined the big league club following the 1977 season.