Jacob Erskine Mayer (born James Erskine Mayer, January 16, 1889 – March 10, 1957) was an American baseball player who played for three different Major League Baseball teams during the 1910s. In his eight-year career, Mayer played for the Philadelphia Phillies, the Pittsburgh Pirates, and the Chicago White Sox. A right-handed pitcher, Mayer's repertoire of pitches included a curveball which he threw from a sidearm angle. As a result of his curveball, then Brooklyn Dodgers manager Wilbert Robinson called Mayer "Eelskine" because the pitch was "so slippery."