McCormick made his major league debut for the Giants on September 3, 1956, at the age of 17, He made two
starts later in the season, and finished with a 0–1
win–loss record and a 9.45
earned run average (ERA) in
innings pitched. The Phillies were able to secure 1 hit (and 1 run) in the bottom of the 6th inning, but the game was called because of the rain. As the 6th inning was never finished, the game statistics reverted to the completion of the last full inning, securing his no-hitter. However, due to a statistical rule change in 1991, no-hitters
must last at least nine innings to count. As a result of the retroactive application of the new rule, this game and
thirty-five others are no longer considered no-hitters. He was acquired along with
Stu Miller and
John Orsino by the
Orioles from the
Giants for
Jack Fisher,
Billy Hoeft and
Jimmie Coker on December 15, 1962. At the end of the 1966 season, McCormick returned to the Giants in a trade that brought
Cap Peterson and
Bob Priddy to the Senators. The 1967 season saw McCormick churn out one of the best statistical years in his career. He led the
National League (NL) in
wins with 22, At the end of the season, McCormick won the
Cy Young Award, garnering 90% of the vote and 18 out of 20 first place votes. In doing so, he became the first Giants pitcher to win the award, and was the only one to do so for 41 years until
Tim Lincecum won it in 2008. McCormick was described, apparently in good faith, as the player who hit the 500th
home run by an MLB pitcher. However, it is unclear how this was calculated, in an age without baseball encyclopedias, and it appears to have been a considerable under-estimate. In contrast, the claim that he was responsible for giving up
Hank Aaron's
500th home run is undoubtedly correct. Because of these two reports, he
personalized his license plate with the words "Mr. 500". ==Personal life==