I was kicking around the idea of looking at the Bears continued use of their "Mug" look on defense.  I even got as far as starting to rough draft some stuff.  Then in my latest Sports Illustrated there was a real good article by Tim Layden about the popularity of the Double A Gap Blitz, and I ceased my writing.  I didn't want to just overkill the concept.  It's definately a good read and worth the time to check out, here's the link, Lasting Impact. 

But I reconsidered and figured I could tackle it anyway, tweak my post, and look at from a Bears perspective.  I'll block quote some snippets from the SI article as I go through my post.

SI credits the Double A Gap look to the late Jim Johnson, one of the better defensive coordinators of all time.  His blitzing schemes, schemes Ron Rivera learned during his tenure as linebackers coach in Philadelphia, gave offenses fits his entire coaching career.  I find it kind of ironic that the Bears didn't start using their Mug look with more regularity until Rivera was relieved of his coordinator duties in Chicago and Bob Babich took over as defensive coordinator.

You can see one particular stroke of Johnson's imagination in any game, on any weekend, and you'll see it in the playoffs too: the Double A Gap Blitz. Two linebackers blitz-or threaten to blitz-from positions on the left and right shoulders of the center (the A gaps), trying to get immediate pressure on the quarterback via the shortest route and forcing the offense into a series of quick and potentially dangerous decisions. "Every team in the league has a Double A Gap Blitz," says Eagles offensive tackle Winston Justice, "and it's a hard thing to block."

When the Bears first started using the look it really was successful for them.  But it didn't take long for teams to simply adjust to a quick hitting slant route, which should have played into their hands...

Also, defensive backs can sit on pass routes, anticipating quick throws that can be jumped for picks.

... but, that would require playing your corners a lot closer to the receiver than the big cushions the Bears defensive backs usually give.

The biggest reason the Bears weren't as successful as they could have been is they went to the look far too often.  Babich dialed up the look a ton in 2007.  He blitzed even more in 2008.  I believe the look, or more particularly, the stubbornness of Babich sticking with it was a big reason for him being demoted to LB coach.  It's funny how he just drove the look into the ground to the point most of us fans couldn't stand seeing him do it, but now it's the trendy look for 4-3 defensive teams.  I didn't think we'd see too much of the look in 2009, but I did notice Lovie Smith went with it a lot more than I thought he would.  Maybe one reason for his use of the Double A Gap Blitz was he had a better blitzer on the field in Hunter Hillenmeyer. 

Lance Briggs and Brian Urlacher are not very adept at blitzing and tend to get caught up in traffic when they're sent.  Hillenmeyer is better at slipping the blocks and getting pressure on the QB when he shoots the A gap.  Hillenmeyer has also looked good when reading the blocking schemes when delay blitzing.  He may have only ended up with 2.5 sacks, but he was ably to get heat on the QB fairly consistently when sent.

It begins most often with the defense's nickel personnel-five defensive backs-on the field with four down linemen and two linebackers in a 4-2-5 configuration (although it can be run from various other sets). As the offense reaches the line of scrimmage, the two linebackers move menacingly into the A gaps. If the quarterback is under center, the 'backers are eye-to-eye with him. "At that point it's mental gymnastics," says Jon Gruden, the former Raiders and Bucs coach who's now an analyst on Monday Night Football. "There's no doubt there's going to be some penetration in the middle if they blitz, and it's going to mess with your blocking schemes."

The Bears do double barrel blitz from time to time, but they also use the look and will drop one if not both linebackers off while blitzing from the edge with a defensive back.  In addition, this season more than in the past I've noticed the Bears dropping their defensive ends into coverage on occasion.  The point is to get the offensive to adjust blocking assignments, then make them react again on the snap.

I thought Lovie started to get more creative with his blitzing and use of some zone blitz concepts in 2009, but he just didn't have the talent for his defense to make an impact.  Having his players back and playing healthy will obviously help, but this team has some glaring holes on the defensive side of the ball that will need to be addressed before they can get back to being anywhere close to their old form.  Who ever ends up calling the defense will need to build on some of these concepts and keep pushing forward.