The gold standard for generosity should be the 2012 New Orleans Saints defense.
No one in NFL history had ever been so amenable, so giving. So bad. New Orleans gave up 7,042 yards in 2012, an all-time worst 440 yards per game.
Enter Rob Ryan, he of the flowing silver mane and the attacking 3-4 scheme. The turnaround was as epic as the defense had been lousy. The 2013 Saints had the fourth-best overall defense in the NFL, the second-best pass defense (194.1 ypg), fourth in sacks (49). No one allowed fewer first downs than New Orleans.
All they've done to get ready for 2014 is add inevitable Hall of Fame cornerback Champ Bailey and Jairus Byrd, one of the best safeties in the free agent market. Once they add more pieces in this year's draft, there's no telling how good this Saints defense could be.