Andrew Jackson Leonard was an Irish born professional baseball player of the 19th century, who played outfield and was also a utility infielder. He played left field for the original Cincinnati Red Stockings, the first fully professional baseball team. He was one of five men to play regularly for both the Cincinnati and the Boston Red Stockings, the latter winning six championships during his seven seasons. He played several infield positions on lesser teams in his early twenties but left field was his regular professional position.

The Cincinnati Red Stockings of 1869 were baseball's first all-professional team, with ten salaried players. The Cincinnati Base Ball Club formed in 1866 and fielded competitive teams in the National Association of Base Ball Players (NABBP) 1867–1870, a time of a transition that ambitious Cincinnati businessmen and ballplayer Harry Wright shaped as much as anyone. Major League Baseball recognized those events officially by sponsoring a centennial of professional baseball in 1969.