Most, I assume, are aware of the fact that Pittsburgh Steelers defensive coordinator Keith Butler was not only formerly a linebackers coach, but also a linebacker himself. He was a second-round draft pick of the Seahawks in 1978 and played there for a decade, starting 132 games as an inside linebacker. He may have never gone to a Pro Bowl, but he was an accomplished player in his own right.
The fact that he was such an experienced player helps him relate to his players, and helps his players respect his wisdom, which is the same advantage that Mike Munchak has with the offensive line or Carnell Lake has with the defensive backs.