Mossi was spotted at an early age and signed by the
Cleveland Indians after leaving high school in 1949. He was assigned to Class-A
Bakersfield. At Bakersfield, Mossi exhibited
control issues; he walked 115 batters in 195 innings in his first year. He nonetheless progressed with his career, posting a 2.92 ERA in 122 innings for the
Wichita Indians in 1951. Mossi was given a spot in the Indians'
bullpen for the 1954 season; as a fifth year professional, major league rules at the time would have forced the Indians to put him through waivers had he not been given a spot on the team. The quality of the Indians' rotation at that time—which included
Early Wynn,
Bob Lemon,
Bob Feller,
Hal Newhouser and
Mike Garcia—meant that Mossi, who had always been a starter, had to be used as a reliever. His major league debut came on April 17 of that year in an 8–1 loss to the
Chicago White Sox as Mossi pitched three innings and allowed one run. The first batter Mossi faced as a major leaguer was future Hall-of-Famer
Nellie Fox, who reached base on an error. His first strikeout was against
Sherm Lollar to end the inning. The Indians were swept in the series, and Mossi pitched four innings in three games, allowing no runs. The following season, he returned to anchoring the bullpen for the Indians. Mossi, along with Narleski and Ossie Alvarez, was traded to the
Detroit Tigers on November 20, 1958 for
Billy Martin and
Al Cicotte. The trade meant that Mossi was guaranteed a spot in a major league starting rotation, something he had missed with the Indians. He went 17–9 with a 3.36 ERA in 1959. In 1960 he went 9–8, albeit on a club that was well below .500, with an ERA of 3.47. Mossi pitched the greatest season of his career in 1961, going 15–7 with a 2.96 ERA on a Tigers club that recorded over 100 wins. It was not long after this that he began to experience problems with his throwing arm, and in his final two years with the Tigers he went 18–20 with a combined ERA of 4.01. before finishing his career in 1965 with the
Kansas City Athletics. During his 12-year major league career, Mossi won 101 games, lost 80 (
.558), and posted an ERA of 3.43. In 460
games pitched, including 165
games started, he registered 55
complete games, eight
shutouts, and 50
saves. He allowed 1,493
hits and 385
bases on balls in 1,548
innings pitched,
striking out 932. Mossi's career
fielding percentage of .990 was the highest ever recorded by a pitcher when he retired. Though never recognized for his defense, he handled 311 chances while committing just three errors. ==After baseball==