[1] Despite bringing a huge bat in the previous season, the decision was made to give Harshman double duty as a pitcher and occasional utility hitter.

Harshman pitched in 26 games with 14 starts, threw a total of 131 innings with 78 strikeouts, a 4.67 ERA, and an average 6–7 win–loss record.

[1] Despite his successful transition from a first baseman slugger to a young phenom pitcher, the Giants allowed the Chicago White Sox to purchase Harshman's contract.

[5] On July 25, he struck out 16 Red Sox hitters, including Ted Williams in a complete game for a 5–2 win.

The record would stand for 32 years until a young flamethrower named Roger Clemens fanned a Major League best 20 batters.

His first full season posted some impressive numbers: a 14–8 won-loss record, a 2.95 ERA, four shutouts, and 134 strikeouts, the latter of which was fifth in the American League.

[1] Harshman found moderate success in the 1955 season by putting up an 11–7 record and a 3.36 ERA while finishing ninth in the AL in strikeouts with 116.

[1] On June 21, 1956, at Comiskey Park, Jack achieved a rarity in Major League Baseball that had only happened twice before in the modern era.

Both he and the opposing Baltimore Orioles starting pitcher Connie Johnson threw a one-hit complete game.

[8] Jack would go on to throw three more shutouts in the season, compiling a 15–12 record with a 3.10 ERA and 143 strikeouts, good enough for eighth in the league.

Following an 8–8 season with the 1957 White Sox,[1] Harshman, Larry Doby and Jim Marshall were traded to the Baltimore Orioles for Billy Goodman, Tito Francona and Ray Moore at the Winter meetings.

[10] Harshman was the first Orioles pitcher to win each of his first five appearances with the ballclub, a feat which was matched by Zach Eflin in 2024.

Harshman began with an 0–6 record and a 6.85 ERA before being traded to the Boston Red Sox for Billy Hoeft on June 15, 1959.

He was forced onto the disabled list on April 24 after checking into the Cleveland Lakeside Hospital to treat problems connected to slipped discs.

On July 24, the Red Sox scored five runs on three hits and four walks before Harshman was pulled after three innings.