As defensive coordinator for the New England Patriots in the 1970s Bullough is credited, along with his college teammate Chuck Fairbanks, with being a significant figure in bringing the 3-4 defense to the NFL. After Fairbanks was suspended prior to the final game of the 1978 season, Bullough's and fellow assistant Ron Erhardt were named co-head coaches for the remainder of the season. After the season Patriots owner Billy Sullivan appointed Erhadt head coach instead of Bullough. Bullough would remain defensive coordinator for one more season with the Patriots.
In 1980, new Cincinnati Bengals head coach and former Green Bay Packers teammate, Forrest Gregg wooed Bullough to install the 3-4 defensive system in Cincinnati. Two seasons later the Bengals would go to the Super Bowl where they fell just short against the San Francisco 49ers. While with the Bengals, Bullough also tutored Dick LeBeau who, not only would succeed Bullough as defensive coordinator but, is credited as the innovator of the 3-4 zone blitz scheme.
Bullough also served as defensive coordinator for the Green Bay Packers (1984)He was named the head coach for the USFL's Pittsburgh Maulers for the 1985 season, but the team folded after the 1984 season; he instead moved on to the Buffalo Bills, where he spent all of the 1985 season (where his team finished in last place) and part of the 1986 season before being fired.
Bullough is considered the "God Father" of Michigan State football. He is married to his wife of 49 years Lou Ann Bullough and they have three kids together, Cheryl, Shane, and Chuck, and 9 grandchildren Corey, Kristi, Jake, Max, Riley, Byron, Holly, Chloe and Annika.