William Henry Spanswick (July 8, 1938 – December 2, 2020) was an American professional baseball player. A left-handed pitcher, Spanswick appeared in 29 games, seven as a starter, in the Major Leagues for the 1964 Boston Red Sox. Spanswick pitched exclusively in relief after June 19, 1964. In 651⁄3 innings pitched, he allowed 75 hits and 44 bases on balls, with 55 strikeouts. The 1964 Red Sox finished eighth in the ten-team American League, with a 72–90 (.444) record. He returned to the minor leagues in 1965 and retired after the 1968 season. He died December 2, 2020, at age 82.