Jeffcoat converted from outfielder to pitcher in 1954 while playing for the Cubs. He worked in 43 games pitched that season, all but three in relief, and would log only four more games in the outfield for the remainder of his major league career. In his debut year on the mound, he won five of 11 decisions and earned seven saves, leading the club. In 104 innings pitched, he posted a poor 5.19 earned run average.
His most successful seasons as a pitcher came from 1955 through 1957. In 1955, he lowered his ERA to 2.95, then won eight of ten decisions in 1956 and recorded ten complete games as a starting pitcher in 1957. Overall, in 245 MLB games pitched, with 51 games started, he posted a win–loss record of 39–37, with 13 complete games, one shutout (a 3–0 six-hitter against the Brooklyn Dodgers at Ebbets Field on June 9, 1957),[3] with 25 saves. In 697 innings pitched, he allowed 772 hits, 365 runs, 327 earned runs, 73 home runs and 257 walks, with 239 strikeouts, 22 hit batsmen, 13 wild pitches, 3,053 batters faced, 35 intentional walks and a 4.22 career earned run average. He is also remembered as the pitcher who beaned Brooklyn's Don Zimmer on June 23, 1956, fracturing Zimmer's cheekbone and ending his season.[4][5]
