coaching should begin before the season starts. Skills, techniques, knowledge need to be developed. Not too mention, if you have been away from the defense, you might not know the details of your players' strengths and weaknesses and how to best use them. Don't know as well where the holes are in your defense and how to cover them.
OK, there is my try. Bronco has shown to be a great defensive mind in my opinion, and it is my hope that the problems we see are very fixable, though they do seem to have not gotten a whole lot better since Bronco took over, but I have a feeling we are trending in the right direction, just takes time.