In 1931 Foster, as a pitcher for the Homestead Grays, recorded a 10–2 record against rival African-American teams. His record against rival African-American teams increases to 11–3, if you count the games that were won and lost in Alcorn, Mississippi, when Syd Pollock's Cubans House of Davids visited Alcorn College prior to Foster joining the Grays. Foster finished the 1931 campaign with J. L. Wilkinson's Kansas City Monarchs where on October 4, 1931 he blew his fastball past a major league all-star team composed of such legendary men as Babe Herman, Joe Kuhel and both Waner brothers, Lloyd and Paul. In the game played at Kansas City's Muehlebach Field, Foster captured a 4–3 win. During the 1931 season, Foster struck out ten men in a game on nine occasions and posted a seasonal high of 16 strikeouts in Vandergrift, Pennsylvania, on August 6. He also recorded four shutouts. Foster finished 1931 with a 23–5 record.