While pitching at Cedarcroft, Pennock threw a no-hitter to catcher Earle Mack, the son of Connie Mack, manager of the Philadelphia Athletics, in 1910. Pennock agreed to sign with the Athletics at a later date. Mack signed Pennock in 1912 to play for his collegiate team based in Atlantic City. Pennock's father insisted that he sign under an alias in order to protect his collegiate eligibility. Pennock threw a no-hitter against a traveling Negro league baseball team, and Mack promoted him to the Athletics. Mack intended for Pennock to be one of the prospects who would replace star pitchers Eddie Plank, Chief Bender, and Jack Coombs.