BVG's defenses struggle against all offenses that cause his players to make adjustments. He runs a pro style D that is way too complicated for college kids. What BVG has yet to realize is these kids have classes, exams, HW, etc. They aren't professionals who have one job, study the playbook.
Max Redfield, (who was just dismissed) had the famous quote about BVG's scheme, "learning Mandarin was easier than his defense." (And yes, Redfield learned Mandarin at ND.)
Brian Kelly said in an interview that Jaylon Smith's job was the eraser, to clean up everybody else's mistakes. That's a waste of a great player. BVG has wasted some great players with his scheme. Most think it is make or break for him this year.