As defensive coordinator for the New England Patriots in the 1970s Bullough is credited, along with his college teammate Chuck Fairbanks, with having been 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 Erhardt head coach instead of Bullough. Bullough would remain defensive coordinator for one more season with the Patriots.