In 2009, the New York Jets owned the best defense in the league. Since Rex Ryan's first season, they've been on a gradual decline as an overall unit. Facts are facts.
The 2013 season was hard to explain because the Jets made tremendous strides in some areas, especially against the run and in the red zone, but they dropped off significantly in pass defense and turnover production.
The defense has evolved under Ryan, going from a coverage-oriented unit with two impact players in the secondary (Darrelle Revis and Antonio Cromartie) to a front-based defense with its best players on the line of scrimmage. That explains the sharp improvement in run defense. In theory, that should have helped them against the pass (i.e. a lot of third-and-long situations), but it never played out that way.
Here's a breakdown:
Final '13 ranking: 19th (387 points)
Final '12 ranking: 20th (375 points)
Total yards allowed
Final '13 ranking: 11th (5,359 yards)
Final '12 ranking: 8th (5,174 yards)
Rushing yards allowed
Final '13 ranking: 3rd (1,412 yards)
Final '12 ranking: 26th (2,138 yards)
Passing yards allowed
Final '13 ranking: 22nd (3,947 yards)
Final '12 ranking: 2nd (3,036 yards)
Final '13 ranking: 13th (36.8 percent)
Final '12 ranking: 12th (37.2 percent)
Final '13 ranking: 4th (44.9 percent)
Final '12 ranking: 25th (58.5 percent)
Final '13 ranking: 31st (15 turnovers)
Final '12 ranking: 18th (23 turnovers)