If you’re looking for a HoF caliber coach you’re looking in the first time HC basket. It’s really rare for HoF caliber HCs to be available for hire after their first HC gig. Don Shula was hired away from the Colts by promoting him from HC to HC/GM/part owner. Vince Lombardi and Bill Parcells came back to coaching after retiring. BillBelichek was fired by Art Modell after the dumpster fire season when the Browns announced they were leaving Cleveland halfway through a season. Paul Brown was sacked after a Power struggle with Art Modell. Edit to add: It’s like trying to find a HoF QB. The best way is in the draft. Once a team has a HoF caliber QB or HC they almost never let them go.