Jacob Nelson Fox was an American professional baseball player. Fox was one of the best second basemen of all time, and the third-most difficult hitter to strike out in Major League Baseball (MLB) history. Fox played in the big leagues from 1947 through 1965 and spent the majority of his career as a member of the Chicago White Sox; his career was bookended by multi-year stints for the Philadelphia Athletics and, later, the Houston Astros.

In baseball and softball, second baseman, abbreviated 2B, is a fielding position in the infield, between second and first base. The second baseman often possesses quick hands and feet, needs the ability to get rid of the ball quickly, and must be able to make the pivot on a double play. In addition, second basemen are usually right-handed; only four left-handed throwing players have ever played second base in Major League Baseball since 1950. In the numbering system used to record defensive plays, the second baseman is assigned the number 4.