Bouton signed with the Yankees as an amateur free agent in 1959. After playing in minor league baseball, Bouton started his major league career in 1962 with the Yankees, where his tenacity earned him the nickname "Bulldog." By this time, he had developed a formidable fastball. He also came to be known for his cap flying off his head at the completion of his delivery to the plate, as well as for his uniform number 56, a number usually assigned in spring training to players designated for the minor leagues. (Bouton later explained that he had been assigned the number in 1962 when he was promoted to the Yankees, and wanted to keep it as a reminder of how close he had come to not making the ball club. He wore number 56 throughout most of his major league career.)