After serving as an assistant with the
San Diego Chargers in 1973, he took a similar position the following year with the
Browns. After head coach
Nick Skorich was dismissed after the 1974 season, Gregg was promoted to head coach in
1975, a position he held through
1977. According to
Dave Logan, safety
Thom Darden and Gregg once had a fist fight after a game. Darden has explained that the
1977 Cleveland Browns did not respond to Gregg's coaching style, which contributed to his firing with one game remaining. In 1977, Darden was one of the vocal dissidents that led to the ouster of Gregg as
head coach of the Cleveland Browns. After sitting out the 1978 season, Gregg returned to coaching in 1979 with the Canadian Football League's
Toronto Argonauts. In
1980, he became the head coach of the Cincinnati Bengals for four seasons through
1983. His most successful season as a head coach was in
1981, when he led the Bengals to a 12–4 regular season record. They defeated the
San Diego Chargers 27–7 in the AFC championship game (known as the
Freezer Bowl), earning them a trip to
Super Bowl XVI, where they lost to the
San Francisco 49ers, 26–21. When his longtime former teammate
Bart Starr was fired after nine years as head coach of the Packers in December
1983, Gregg was allowed out of his Bengals' contract to take over in Green Bay. He finished his NFL coaching career with the Packers, leading them for four seasons,
1984–
1987, with a record of 25–37–1. Gregg's overall record as an NFL coach was 75 wins, 85 losses and one tie. He was also 2–2 in playoff games, all with the Bengals. He is one of only two coaches, the other being
Marvin Lewis, to have left the Bengals with a winning record. Gregg resigned from the Packers in January 1988 and took a pay cut to take over at SMU, his alma mater. He was brought in to revive the Mustang football program after it received the "
death penalty" from the NCAA for
massive violations of NCAA rules. Gregg knew that any new coach would be essentially rebuilding the program from scratch, but when acting president William Stalcup asked him to return, he felt he could not refuse. As it turned out, when Gregg arrived, he was presented with a severely undersized and underweight roster composed mostly of freshmen. Gregg was taller and heavier than nearly the entire 70-man squad. The team was so short on offensive linemen that Gregg had to make several wide receivers bulk up and switch to the line. By nearly all accounts, it would have been unthinkable for the Mustangs to return for the 1988 season under such conditions. In
1989, the Mustangs went 2–9, including a 95–21 thrashing by
Houston—the second-worst loss in school history. In that game, eventual
Heisman Trophy winner
Andre Ware threw six touchdown passes in the first half, and
David Klingler added four more in the second, even with the game long out of reach. Gregg was so disgusted that he refused to shake Houston coach
Jack Pardee's hand after the game. Nonetheless, Gregg reflected fondly on the experience. In a 2012 interview with
The New York Times, he said the players on the two teams he coached should have had their numbers retired for restoring dignity to the program. "I never coached a group of kids that had more courage," he said. "They thought that they could play with anyone. They were quality people. It was one of the most pleasurable experiences in my football life. Period." and he served as athletic director until 1994. He returned to the CFL with the
Shreveport Pirates in 1994–95, during that league's
brief attempt at expansion to the
United States. His overall record in the CFL was 13–39. When former Shreveport Pirates owner
Bernard Glieberman bought a stake in the
Ottawa Renegades in May 2005, Gregg was appointed Ottawa's vice president of football operations, a position he held through 2006. ==Personal life==