The Jacksonville Jaguars employed the worst defense in the NFL by our rankings last season: they finished dead last in DVOA (minus-21.2 percent), and their renowned run defense (which had been in the top 10 in our rankings in 2008 and 2009) slipped to 28th in the league. This season, they've vaulted all the way to the second best defense in the league, which is a historic jump by DVOA standards.
Jacksonville's swing in DVOA (minus-35.2 percent) has been the largest year-to-year improvement since the 1998 Dolphins (minus-33.6 percent).
While I expected the run defense to get back to its lofty heights after the Jaguars brought in Paul Posluszny and Clint Session this offseason, the pass defense still looked shaky on paper when I wrote the Jacksonville chapter in "Football Outsiders Almanac 2011." Rashean Mathis was coming off one of the worst seasons of his career, Derek Cox hadn't developed and Dawan Landry could fill only one safety hole -- that left some combo of Courtney Greene and rookie Chris Prosinski manning the other spot.
However, Landry has been excellent, and the Jaguars made a minor trade that has paid enormous dividends for them.