star pitchers Eddie Plank, Chief Bender, and Jack Coombs. Pennock made his major league debut with the Athletics during their 1912 season on May 14, allowing one hit in four innings pitched. He was the youngest person to play in the American League (AL) that season. Former major leaguer Mike Grady, a neighbor of Pennock's in Kennett Square, took Pennock under his wing, while Bender taught Pennock to throw a screwball. Pennock missed most of the 1913 season with an illness, but was able to rejoin the team late in the season. In the 1914 season, Pennock posted an 11–4 win–loss record with a 2.79 earned run average (ERA) in innings pitched for the Athletics, and pitched three scoreless innings in the 1914 World Series, which the Athletics lost to the Boston Braves. Mack let Bender go after the season, naming Pennock his Opening Day starting pitcher in 1915. On Opening Day, Pennock threw a one-hit complete game shutout against the Boston Red Sox. However, as the Athletics struggled, Pennock's nonchalant playing style drew Mack's ire. Concluding that Pennock "lacked ambition", Mack sold Pennock to the Red Sox for the waiver price of $2,500 ($ in current dollar terms). Mack later regarded this sale as his greatest mistake. Boston Red Sox With a deep pitching staff in place, the Red Sox loaned Pennock to the Providence Grays of the International League in August for the remainder of the 1915 season. He split the 1916 season between the Red Sox and the Buffalo Bisons, also in the International League. With Buffalo, Pennock pitched to a 1.67 ERA, as Buffalo won the league pennant. Though the Red Sox won the 1915 and 1916 World Series, Pennock did not appear in either series. Pitching in minor league baseball, Pennock began to regain confidence. However, Boston manager Jack Barry used Pennock sparingly in the 1917 season, and Pennock enlisted in the United States Navy in 1918. Pennock pitched for a team fielded by the Navy, defeating a team composed of members of the United States Army in an exhibition for George VI, the King of England, in Stamford Bridge. After the game, Ed Barrow, the new manager of the Red Sox, signed Pennock to a new contract after promising to use him regularly during the 1919 season. Pennock received only one start apiece in the months of April and May, as the 1919 Red