Foster Leroy Witherup (July 26, 1886 – December 13, 1941) was an American professional baseball pitcher.

He played all or part of three seasons in Major League Baseball between 1906 and 1909 for the Boston Beaneaters (1906) and Washington Senators (1908–09).

Listed at 6 ft 0 in (1.83 m), 185 lb., Witherup batted and threw right-handed.

In a three-season career, Witherup posted a 3–12 record with a 4.44 earned run average in 26 appearances, including 17 starts and 12 complete games, giving up 80 earned runs on 189 hits and 47 walks while striking out 71 in 162+1⁄3 innings of work.

This biographical article relating to an American baseball pitcher born in the 1880s is a stub.