First, if you haven't yet, check out Bob Gretz's article on Romeo Crennel. It gives quite a bit of background information on the man that is expected to be announced the next defensive coordinator of the Kansas City Chiefs.
For example, did you know that he has a sister named Juliet? Yep, from Romeo and Juliet.
Back to football. Gretz also includes a couple of interesting quotes from players that played under Crennel.
Carl Banks was a linebacker with the New York Giants for much of the time Crennel was there in the 80s. He suggests it's not all Bill Belichick, the defensive coordinator at the time, when it comes to the defensive genius.
"A lot of what Bill Belichick is now is as a result of having very smart coaches and players around him. As far as coaching, Romeo is just as much of a defensive genius as Bill."
"In the meetings, Romeo calls the defenses and runs the entire defense. Bill Belichick puts in the flavor and makes suggestions, but the defense is Romeo’s."
So, not everyone thinks the defense in New England and New York was all Belichick.