Rube Foster

In 1902, Foster moved to Chicago, where he joined the Chicago Union Giants, better known as the Leland Giants for owner Frank Leland, a veteran of black baseball. The same year, he moved to Philadelphia and switched to E. B. Lamar's Union Giants, or Cuban Giants. Around this time he outpitched the Philadelphia Athletics's star pitcher Rube Waddell in an exhibition game, earning himself the nickname "Rube" as a trophy. It would stick with him for the rest of his life.

In 1903 he switched to a rival Philadelphia team, the Cuban X-Giants, pitching that fall in black baseball's first World Series, which the X-Giants won five games to two. Legend has it that the same year McGraw asked Foster to teach his "fadeaway" screwball pitch to his New York Giants pitchers Christy Mathewson, Iron Man McGinnity, and Red Ames. Soon afterward, the Giants rose from last place in the league to second.

In 1904, Foster and most of the X-Giants team switched back to the Union Giants and won the three-game World Series over their former team. Statistics on Foster are often missing or sketchy and the truth is hard to determine, but for 1905 he is noted to have won 51 out of 56 games. Unhappy with his pay by 1906, Foster left Philadelphia to rejoin the Leland Giants in Chicago, where he offered to both play for and manage the team. Bringing seven of his best players with him, including power hitters John Henry Lloyd, Grant "Home Run" Johnson, and Pete Hill, Foster persuaded Frank Leland to fire his team members and hire Foster's. The new team won the Chicago semipro title in 1907, winning 110 out of 120 games, with 48 consecutive wins. In a postseason series against the Chicago City All-Stars, a white team that hired major and minor league players, Foster pitched four winning games, and his team finished first.

Foster's pitching skills were by this time so finely tuned that Hall of Famer Honus Wagner once called him "one of the greatest pitchers of all time … smartest pitcher I've ever seen." Chicago Cubs manager Frank Chance called him "the most finished product I've ever seen in the pitcher's box." Foster was a big man, standing six feet four inches tall and weighing between 224 and 260 pounds. Although the fans loved him, many players were said to dislike or even fear him because he "engaged in personalities" when he pitched and often carried his Texas six-guns. He unnerved players by smiling and appearing jovial and unconcerned on the field. He often distracted batters and tricked them into striking out. His searing fastball and powerful underhand screwball made him a star pitching attraction of black baseball and the envy of many white pitchers.