Calvin Lee Koonce (November 18, 1940 – October 28, 1993) was an American professional baseball player, a right-handed pitcher in the Major Leagues from 1962–1971 for the Chicago Cubs, New York Mets and Boston Red Sox. Born in Fayetteville, North Carolina, he attended Campbell University. Koonce stood 6 feet 1 inch (1.85 m) tall and weighed 185 pounds (84 kg).
Koonce appeared in 334 Major League games pitched, all but 90 as a relief pitcher. He allowed 972 hits and 368 bases on balls in 971 innings pitched, with 504 strikeouts and 24 saves. He recorded 11 saves and a low 2.42 earned run average for the 1968 Mets, and was a member of the Mets' 1969 World Series championship team, but he was less effective during the regular campaign and did not appear in the postseason.
After retiring as an active player, he was head baseball coach of Campbell University, his alma mater, for seven seasons (1980–1986), and a minor league executive. He died from lymphoma at age 52.