Westrum set an International League record in 1949 by hitting five grand slams, though he played in only 51 games. In 1950, his first year as a Giants regular, he hit 23 HR, set an NL record for catchers with a .999 fielding average (broken by Charles Johnson in 1997) and led the league in assists and double plays. He caught every game for the Giants in the 1951 and 1954 World Series.
After coaching for San Francisco from 1958 through 1963, Westrum was involved in the only trade of coaches in major-league history, going to the Mets for Cookie Lavagetto. When Mets manager Casey Stengel broke his hip during the 1965 season, Westrum replaced him and remained at the helm through 1967. He managed the Giants in 1974 and 1975, finishing third in ’75.