Hornsby came to the attention of the St. Louis Cardinals during an exhibition series between that team and the Railroaders in spring training in 1915. Cardinals' manager Miller Huggins told his only scout, Bob Connery, to look for minor league players to fill the roster of their financially struggling team. In September, the Cardinals purchased Hornsby's contract from Denison and added him to their major league roster, although his only professional baseball experience had been in Class D. Hornsby's first game came on September 10, when he relieved Art Butler at shortstop in a 7–1 loss to the Cincinnati Reds. Three days later he started a game, and he got his first hit the next day against Rube Marquard of the Brooklyn Robins. Hornsby finished the season with a .246 average in 57 at-bats while the Cardinals finished in sixth place in the National League (NL). At only 19 years old, Hornsby was the fourth-youngest player in the NL that year.