When Rex Ryan arrived in Buffalo last January, few expected that one of the NFL's most highly regarded defensive minds wouldn't be able to keep one of the league's top-performing defenses last season playing at a high level.
Yet despite losing only safety Da'Norris Searcy in free agency and adding one of the NFL's best rookies, cornerback Ronald Darby, in the draft, the Buffalo Bills' defense has largely been in a tailspin since allowing 507 yards in a Week 2 loss to the New England Patriots.
Injuries -- most notably a lingering neck injury to safety Aaron Williams and a season-ending knee injury to defensive tackle Kyle Williams -- have played a role, but the losses in personnel don't fully explain why a unit that allowed fourth-fewest points and yards per game last season has suddenly plummeted to 21st in yards allowed and 17th in points allowed this season.