Maligned as a “five-inning pitcher” and a hypochondriac early in his career, Pappas reached double figures in wins every year but one from 1958 to 1972, but he is best remembered as part of one of the worst trades in Reds history, when he was acquired with journeymen Jack Baldschun and Dick Simpson for Hall of Famer Frank Robinson after the 1965 season. Despite a good fastball and hard slider, the consistent righthander never achieved the stardom many felt he was capable of, yet when he retired he was only one NL victory shy of 100 in each league, and he won 209 ML games without ever winning more than 17 in a single season.
Pappas pitched only three games in the minors before going 10-10 as a 19-year-old rookie for Baltimore in 1958, and was 15-9, 3.27 in 1959, but had already earned a reputation as a brash, impetuous youngster. He would show up the umpires with his griping and posturing on the mound, and once called the press box during a game to complain about an official scorer’s decision that had cost him four earned runs. He also had trouble completing his starts, but still averaged nearly 15 wins a season for the Orioles from 1960 to 1964. Pappas tossed seven shutouts (including a one-hitter against the Twins) on the way to a 16-7 record in 1964, and started the All-Star Game for the AL in 1965, then was traded to the Reds in the off-season. In Cincinnati, he went only 12-11, 4.29 in 1966 while Frank Robinson was winning the Triple Crown in Baltimore, and after a 16-13 season in 1967 he was traded to the Braves the following year.
Pappas compounded his reputation problems by frequently squabbling with management as a player representative, but in time he did tone down his on-field antics considerably, and after the Braves sold him to the Cubs in 1970 he enjoyed two of his better ML seasons. He was 17-14 in 1971, but with a career-high 14 complete games and an NL-best five shutouts, and in 1972 he was 17-7 with a 2.77 ERA. On September 2, 1972, he was one out away from a perfect game against the Padres when he walked Larry Stahl, but settled for an 8-0 no-hitter. He retired after going 7-12 in 1973.
Pappas was also dangerous at the plate with 20 career home runs, including two in one game August 27, 1961.