If you’ve been wearing out your Greg Mattison dartboard over the last several weeks, you’re probably not alone. After all, the current Ravens defensive coordinator is solely responsible for the fall of a once-dominant unit all the way to 10th in the NFL, right? (As an aside, how spoiled are we to be frustrated with a unit still better — statistically — than 22 other defenses in the league?) From eliminating the submissive three-man rush to playing tighter, press coverage in the secondary, Marvin Lewis, Mike Nolan, or Rex Ryan would be coaching this defense to the elite level it enjoyed over the last decade instead of the mortal status it currently holds. If only it were that simple. Placing blame on a few individuals is common practice (Mattison, maligned cornerback Fabian Washington, and, until recently, “overrated” linebacker Terrell Suggs are popular targets these days), but the defensive problems run far deeper. Personnel issues, aging stars, a key injury (anyone remember Domonique Foxworth?), and — perhaps — coaching shortcomings have left the Ravens with an above-average defense pursuing ghosts of dominance on the M&T Bank Stadium turf. Truth be told, the current deterioration of the Baltimore defense began years ago,