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.)

Bouton appeared in 36 games during the 1962 season, including 16 starts, and had a win-loss record of 7–7.
He did not play in the Yankees' 1962 World Series victory over the San Francisco Giants, although he had originally been slated to start Game 7.
When the game was postponed a day because of rain, Ralph Terry pitched instead.
Bouton went 21–7 and 18–13 in the next two seasons, and appeared in the 1963 All-Star Game.

A memorable duel between Bouton and Don Drysdale of the Los Angeles Dodgers occurred in Game 3 of the 1963 World Series before a crowd of 55,912 at Dodger Stadium.
Drysdale pitched a three-hit shutout in a 1–0 victory, Bouton giving up just four hits for the Yankees.
The only run scored in the first inning on a walk, wild pitch and single by Tommy Davis that bounced off the pitching mound.

Bouton won both his starts in the 1964 World Series.
He beat the St. Louis Cardinals 2–1 with a complete-game six-hitter on October 10 on a walk-off home run by Mickey Mantle, then won again on October 14 at Busch Stadium, 8–3, backed by another Mantle homer and a Joe Pepitone grand slam.
He was 2–1 with a 1.48 ERA in World Series play.

Bouton's frequent use by the Yankees during these years (he led the league with 37 starts in 1964 in addition to pitching in that year's World Series) probably contributed to his subsequent arm troubles.
In 1965, an arm injury slowed his fastball and ended his status as a pitching phenomenon.
Relegated mostly to bullpen duty, Bouton began to throw the knuckleball again, in an effort to lengthen his career.
By 1968, Bouton was a reliever for the minor league Seattle Angels.

In October 1968, Bouton joined a committee of American sportsmen who traveled to the 1968 Summer Olympics, in Mexico City, to protest the involvement of apartheid South Africa.

In 1969, the expansion Seattle Pilots signed Bouton and used him almost exclusively out of the bullpen.
On May 16, he pitched three innings of hitless, scoreless relief at Fenway Park.
The Pilots scored six in the top of the 11th inning to earn him the win, even though other Seattle relievers gave five runs back in the bottom of the 11th.
Bouton earned another win in July against the Red Sox with 1⅓ innings of relief, again not allowing a hit.
Over 57 appearances with the Pilots, he compiled a 2-1 record with a 3.91<https://www.baseball-reference.com/players/b/boutoji01.shtml> ERA.

The Pilots traded him to the Houston Astros in late August, where Bouton had a 4.11<https://www.baseball-reference.com/players/b/boutoji01.shtml> ERA in 16 appearances.
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.)
Bouton appeared in 36 games during the 1962 season, including 16 starts, and had a win-loss record of 7–7. He did not play in the Yankees' 1962 World Series victory over the San Francisco Giants, although he had originally been slated to start Game 7. When the game was postponed a day because of rain, Ralph Terry pitched instead. Bouton went 21–7 and 18–13 in the next two seasons, and appeared in the 1963 All-Star Game.
A memorable duel between Bouton and Don Drysdale of the Los Angeles Dodgers occurred in Game 3 of the 1963 World Series before a crowd of 55,912 at Dodger Stadium. Drysdale pitched a three-hit shutout in a 1–0 victory, Bouton giving up just four hits for the Yankees. The only run scored in the first inning on a walk, wild pitch and single by Tommy Davis that bounced off the pitching mound.
Bouton won both his starts in the 1964 World Series. He beat the St. Louis Cardinals 2–1 with a complete-game six-hitter on October 10 on a walk-off home run by Mickey Mantle, then won again on October 14 at Busch Stadium, 8–3, backed by another Mantle homer and a Joe Pepitone grand slam. He was 2–1 with a 1.48 ERA in World Series play.
Bouton's frequent use by the Yankees during these years (he led the league with 37 starts in 1964 in addition to pitching in that year's World Series) probably contributed to his subsequent arm troubles. In 1965, an arm injury slowed his fastball and ended his status as a pitching phenomenon. Relegated mostly to bullpen duty, Bouton began to throw the knuckleball again, in an effort to lengthen his career. By 1968, Bouton was a reliever for the minor league Seattle Angels.
In October 1968, Bouton joined a committee of American sportsmen who traveled to the 1968 Summer Olympics, in Mexico City, to protest the involvement of apartheid South Africa.
In 1969, the expansion Seattle Pilots signed Bouton and used him almost exclusively out of the bullpen. On May 16, he pitched three innings of hitless, scoreless relief at Fenway Park. The Pilots scored six in the top of the 11th inning to earn him the win, even though other Seattle relievers gave five runs back in the bottom of the 11th. Bouton earned another win in July against the Red Sox with 1⅓ innings of relief, again not allowing a hit. Over 57 appearances with the Pilots, he compiled a 2-1 record with a 3.91<https://www.baseball-reference.com/players/b/boutoji01.shtml> ERA.
The Pilots traded him to the Houston Astros in late August, where Bouton had a 4.11<https://www.baseball-reference.com/players/b/boutoji01.shtml> ERA in 16 appearances.
Jim Bouton