Kingman made his MLB debut with the Oakland Athletics on June 28, 1979. During his rookie season, he appeared in 15 games, starting 10 of them. He finished the year with a 2-5 record and a 4.10 ERA, showing potential as a starting pitcher. The following year, 1980, proved to be the most memorable of his career. Kingman became the last pitcher in the 20th century to lose 20 games in a single season, ending with an 8-20 record. Despite the losses, he pitched 211 innings and maintained a 3.83 ERA, indicating that he often received little run support from his team.
In 1981, Kingman continued to be a part of the Athletics' starting rotation. The season was shortened due to a players' strike, and Kingman finished with a 3-6 record and a 3.84 ERA over 16 games. His performance remained consistent, but the team struggled to provide offensive backing, which affected his win-loss record.
The 1982 season saw Kingman transitioning to a relief role. He appeared in 24 games, starting only 4, and posted a 4.48 ERA. His adaptability to different pitching roles was evident, although his opportunities to start games diminished. In 1983, Kingman was traded to the Boston Red Sox, but he did not appear in any games for them. He spent the season in the minor leagues before retiring from professional baseball.
Throughout his career, Kingman was known for his durability and ability to pitch deep into games.
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