Plaza, who was entering his 30th season in the role and his 61st in professional baseball as a player, coach and manager, passed away at the age of 77 in St. Petersburg, Fla., where he had recently suffered a series of small strokes and was being treated at a rehab nursing home.
"On behalf of the A's, I send my deepest condolences out to the Plaza family," A's general manager Billy Beane said in a statement. "Ron was a great baseball man and a wonderful person. His love of the game and dedication to teaching were unmatched during his 30 years with the A's. All of us -- front office, staff, and players -- are richer for having been around Ron for so long. He will be missed by everyone in the organization."
In addition to his instructor role, Plaza played an integral part in helping establish the A's training complex in the Dominican Republic and was given credit for aiding in the development of Latin American players such as shortstop Miguel Tejada and catcher Miguel Olivo, both of whom signed as amateur free agents with Oakland in the 1990s.
Plaza joined the Oakland organization in 1983 after 14 years with the Reds. He served as the Reds' Minor League roving instructor from 1970-77 before serving on the Major League coaching staff for six seasons (1978-83).
He also managed at various levels in the Cardinals' organization from 1963-68, and was named Florida State League Manager of the Year in 1967. Plaza was an infielder in the Cardinals' Minor League system for 12 years (1951-62), including six seasons at the Triple-A level.
"Ron had a pure love of baseball and demonstrated it as a passionate teacher and contributor to the game," A's director of player development Keith Lieppman said. "He left an important legacy, not only with the A's organization, but with the impact he had on the many lives he touched throughout his career. He elevated players and staff through his knowledge and his ability to get the most out of them. The game has lost one of its great teachers."