2015 Rank: 29
2014 Rank: 13
Fall: 16 spots

After losing Patrick Willis, Justin Smith, Chris Borland, and Aldon Smith, the 49ers' defense turned from one of the league’s best to one of its worst.

True, the 49ers had dropped out of the top 10 in 2014, but the fall down to 29th in 2015 was surely a disappointment. There isn’t much to talk about except NaVorro Bowman. Notching his fourth First-Team All-Pro selection in his first action since a knee injury in the 2014 NFC Championship Game, Bowman led the NFL with 154 tackles, 69 more than the 49er with the second-most tackles on the team.