On March 26, 2015, it was announced that Gruden would serve as the inaugural head coach for the Flint Firebirds of the Ontario Hockey League during the 2015–16 season. In a highly publicized incident, he was fired a month into the season. Reports claim the firing was due to refusing to increase the playing time of defenseman Håkon Nilsen, the team owner's son, however team president Costa Papista denied the reports. Following a successful player walkout, Gruden was reinstated as the Firebirds head coach and given a three-year contract extension. On February 17, 2016, Gruden was again fired by the Firebirds. On June 3, 2016, Gruden was named head coach of the Hamilton Bulldogs. Following the 2017–18 regular season, he led the Bulldogs as the OHL playoff champions.