-Biggest thing that has hurt us is the lack of a solid second corner. DMilli is an elite cover corner, but I think he realizes at times he is our only playmaker in the secondary. That causes him to take more chances, and it gets burned more than he normally would. Belue is ok, but he lacks the instinct that a corner needs to succeed at a higher level, and beyond those two, we have no depth. Not only do we not have a solid second corner, we haven't had a solid nickel corner emerge either. Fulton has never really developed, and Vinnie just isn't athletic enough to have to fill that role. Think about last year, we had Dre, Dee, and throw in Menzie there, and you have an almost impenetrable wall in the secondary. 09 had Arenas, Jackson, and a couple of others who contributed heavily. This year, we just haven't really had anyone else step up, and that to me is our biggest problem.
-Another thing that has hurt us is the disappearance of Robert Lester. At one point he was one of the best ball hawking safeties in the game. He was an All-American type talent, and he was supposed to be one of the leaders on our defense. He's had his moments this year, but for the most part he has been almost invisible. I can probably count on one hand the number of times I have heard his name called this year, and he is far to talented not to making a difference. For our secondary to succeed, we really need Lester to play up to the levels that we all know he can.
-A lot of our tackling issues have been because of poor angles being taken by the defense. Sometimes they are trying to hard to make a huge play instead of making a sure tackle, sometimes they are just underestimating the speed of the offense. Either way it's an easy mistake to fix, and we haven't done it yet.
My two cents, and there are probably other reasons, but those are the biggest ones that stand out to me.