George Barclay "Win" Mercer (June 20, 1874 – January 12, 1903) was a pitcher in Major League Baseball from 1894 to 1902. Born in East Liverpool, Ohio, he played primarily with the National League Washington Senators (1894–1899), winning 20 games twice with the club. He also played with the New York Giants (1900), the American League Washington Senators (1901), and the Detroit Tigers (1902). Mercer led the National League in games started (41), shutouts (3), and saves (3) in 1897. He holds the interesting record of most stolen bases (nine) by a pitcher in one season. His career record of 251 complete games ranks No. 77 in Major League history.