He played professional baseball as a pitcher from 1965 to 1982, including 15 seasons in Major League Baseball with the Washington Senators (1965–70), Detroit Tigers (1971–76), Chicago Cubs (1976), Oakland Athletics (1977–78), Toronto Blue Jays (1978), San Francisco Giants (1979) and Pittsburgh Pirates (1979).

[3] In high school, Coleman was considered "an overpowering pitcher" who was "watched enviously by major league scouts.

[5] After a 12-game stint with the Burlington Senators in the Carolina League, Coleman made his Major League Baseball debut at age 18, less than four months after graduating from high school, on September 28, 1965, throwing a four-hitter against the Kansas City Athletics and pitched two complete game victories in the final week of the 1965 season.

[2] Coleman spent most of the 1966 season with the York White Roses in the Eastern League, compiling a 7–19 record in 32 games.

[8] In 1967, Coleman won a spot in the Senators' starting rotation, appeared in 28 games, and compiled an 8–9 record with a 4.63 ERA.

[3] On March 27, 1971, Coleman was knocked unconscious by a line drive hit by Ted Simmons of the St. Louis Cardinals during a spring training game.

[9] Coleman sustained a linear skull fracture, was hospitalized for two weeks, and remained on the disabled list for 21 days before joining the Tigers in May 1971.

His 236 strikeouts in 1971 was a career high and ranked third in the American League behind Mickey Lolich and Vida Blue.

[3] Only four American League pitchers – Wilbur Wood (70), Jim Palmer (63), Mickey Lolich (63), and Catfish Hunter (63) – had more wins than Coleman over those same three years.

On April 11, 1974, Coleman lost a bid for a no-hitter in the eighth inning when Gene Michael of the New York Yankees hit a one-out single.

He walked an astounding 158 batters in 1974 (a Tigers single-season record) for a career high rate of 5.0/9 IP.

[25] Prior to the 1978 season, Oakland owner Finley again sought to discard Coleman, asking him to report to the Athletics' minor league club in Vancouver.

Finley reportedly "blew his top" after Coleman gave up a home run to Chicago's Lamar Johnson.

Bobby Winkles resigned as Oakland's manager after Finley's impulsive decision to sell the club's most effective relief pitcher.

"[25] Despite not fitting into the Blue Jays' plans, Coleman compiled a 2–0 record in 31 relief appearances for the club.

[3] After a strong 1978 season, Coleman announced in late October 1978 that he would not return to Toronto and that he intended to become a free agent.

[3] After being released by the Giants, Coleman signed in May 1979 with the Portland Beavers, the Pittsburgh Pirates' Triple A affiliate in the Pacific Coast League.

[31] During the Pirates' pennant drive in the second half of the 1979 season, Coleman made 10 relief appearances and compiled a 6.10 ERA in 20+2⁄3 innings pitched.

Coleman joked about the foibles of his young players after arriving in Peoria:"One game, my right fielder dropped a fly ball.

The runner was on third by the time he gets to the ball, but he launches it and it lands in the left field corner at the foul pole.

In 1987, he was the organization's roving minor-league pitching instructor, and in 1988 he joined the Angels' major league staff as bullpen coach.

[35] In 1991, Coleman left the Angels to become the pitching coach for the St. Louis Cardinals under manager Joe Torre.

In October 1994, the Cardinals opted not to renew Coleman's contract in a front office shakeup that also saw the arrival of a new general manager and the departure of Bucky Dent as the club's third-base coach.

In 2001, Coleman was hired as the pitching coach for the Durham Bulls, the Triple A affiliate of the Tampa Bay Rays.

[40] The 2014 season marked Coleman's 50th year working in professional baseball as a player, scout, coach, instructor or manager.

[41] Their son, Casey Coleman, was born in Fort Myers in 1987 and pitched in Major League Baseball for the Chicago Cubs from 2010 to 2012 and for the Kansas City Royals in 2014.