In 1956 every major league club was after this overpowering 17-year-old who had posted a 49-4 American Legion record, including four no-hitters and a 26-strikeout performance. The Giants signed McCormick for a reported $60,000 bonus and, under the rules of the time, had to bring him right to New York. Scared and wild, he lasted just three innings in his first start. In 1957, pitching mostly in relief, he became the youngest modern NL pitcher (18) to record three wins.
As McCormick matured, he gained greater success. On June 12, 1959, he threw a five-inning no-hitter against Philadelphia. He was the NL ERA leader in 1960 (2.70) when he went 15-12. But he dropped to 13-16 in 1961 when he allowed a league-high 33 home runs. He was plagued by arm trouble through 1962, and the hot-tempered pitcher was traded to Baltimore.
McCormick was returned to the minors before rebounding with the 1965 Senators. He recorded marks of 8-8 and 11-14 and was reacquired by the Giants in December 1966. He had lost his blazing fastball, but had mastered his breaking pitches and developed a screwball. In 1967 he went 22-10 (2.85), leading the NL in wins, and won the Cy Young and Comeback Player of the Year awards. Over the next two-plus seasons, he went 26-27 for San Francisco. He finished up in the Pacific Coast League.