APC's fearless leader posted this in his take on McCarthy's latest press conference:

The problem with the run defense is that they're trying to hard? I'm not buying that lemon.

Buy that lemon, Brandon!  From my experience, the "My biggest weakness is that I work too hard" sentiment is true.  And I can prove it...sorta.

Here's how it happens: you get defensive players that, as individuals, are strong against the run.  I reference players like Ryan Pickett, Aaron Kampman, Johnny Jolly, A.J. Hawk and Atari Bigby (when healthy).  Not to say that the rest of the defense sucks against the run (except for KGB), but these guys are particularly skilled.

Then, those individuals form a unit of 11, go through training camp and practice, and everything is all about gap control and responsibilities.  When executed correctly, the run defense is foolproof because you always have enough players to control all the gaps.  I would argue that the Packers had a unit like this at the beginning of the season.

However, when one player misses an assignment, it's like a crack in the levee, and the run defense breaks.  And when that happens, the players that are usually stout against the run try to cover their responsibilities and the neighboring player's responsibilities.  This is what McCarthy means by players "doing too much".  By taking on additional responsibility, they leave themselves spread too thin, which results in a domino effect and the subsequent breakdown of the entire system.

 That's what's been happening this season so far, and a perfect example is Nick Barnett.  As noted on this site, Barnett has been M.I.A. this season, and I think this is exactly what's happened.  As the injuries pile up, Barnett (the leader of the defense) says to himself "That's OK, I can handle both gaps."  I call this the "superhero effect", where a player puts too much stock in his abilities and tries to 'save the world', as it were. 

But Nick Barnett is no Superman.  There are maybe one or two players in the entire league who can manage this (my mind jumps to Ray Lewis circa 2000).  So now he's playing two gaps instead of the one he should be focused on, and misses an assignment.  Then another player tries to cover the gap Barnett missed on the next play.  Then another player tries to cover that gap, and so on, and so forth.

How is this problem solved?  Two things: personal discipline from the players and general discipline from the coaches.  The coaches have to install the system and maintain it throughout practice, and the players have to be level-headed enough to buy into the gameplan and avoid the "superhero effect".

That's my take on McCarthy's statement during his press conference.  But maybe I'm wrong.  Perhaps I'm just adding a lot of sugar to make lemonade.