According to Tim Layden's Blood, Sweat and Chalk, the Double A Gap blitz was brought into the modern NFL by the late Jim Johnson, Defensive Coordinator for the Philadelphia Eagles from 1999-2008. Here's an excerpt:
The Double A Gap came in 2001, it was Johnson's ultra-aggressive extension of everything he'd been doing. First conjured when Johnson asked himself this question: Instead of a single blitzer on the edge or a single blitzer in the middle, why not load up the middle of the formation? The first time Johnson called it in a game, Eagles defensive end Darwin Walker cam unblocked for a sack. From 2000 to '08, the Eagles had 390 sacks, second in the NFL.
- Blood, Sweat, and Chalk by Tim Layden, Page 227.
See below for an example of what the Double A Gap blitz looks like. The A Gaps are gaps on the Offensive Line between the Center and Guards.
The appeal of the Double A Gap blitz comes from simplicity. It places 2 potentially unblocked blitzers directly in front of the QB. And as a result, the offense facing the blitz has to make a decision. If you choose to look at it from a military vantage, it embodies Superiority at the Point of Contact, Simplicity, and Movement-Mobility. It's a tactic which constrains what the offense can do should they meet it head-on.
Here are the offense's blocking options, again, from Blood, Sweat and Chalk, Page 228:
- Gap protection, in which both guards block down inside, putting three big bodies on the two blitzing linebackers. This, however, forces the offensive tackles to block down as well to pick up the two defensive tackles, and it leaves some combination of running backs and tight ends to deal with edge-rushing defensive ends.
- Slide protection, in which the entire offensive line slides one way, with the center picking up one blitzer and one guard picking up the other. The same problem results, with one defensive end left rushing against a running back, or, a best, a tight end or H-back.
- Straight protection, in which the center takes one blitzer, and the other one is allowed a free release to the running back, who must make a key block in the quarterback's lap.
Because the Double A threatens to bring pressure so close to the quarterback and so quickly, the offense must adjust to one of the above protections on the assumption that the A Gap rushers are going to blitz.- Pages 228-229.
Figure 3: 2:55 left in the 1st quarter. 3rd and 10 at the SD 20. This is the second time the Vikings show a Double A blitz. The Vikings, however, add an interesting wrinkle. Both linebackers blitz while LDE Brian Roberson drops back into zone coverage. The Chargers elect to block this one straight, and I can't think of a play that better illustrates Danny Woodhead's value as a blocking RB. He steps up and pick ups one of the blitzers, and buys enough time for Rivers to get rid of the ball. Unfortunately, Rivers double clutches, and LB Anthony Barr eventually sheds a Watt/Franklin double-team and the result is a sack and fumble, recovered by the Vikings.
Figure 4: 13:34 left in the 3rd quarter. 3rd and 7 at the SD 23. By this time in the game (early 3rd quarter), the Vikings have shown more Double A pressures than the Bengals did all game. The Vikings have also been much more aggressive with their blitzes, as this is the 6th time they've sent both linebackers - although this time LB Eric Kendricks delays a moment before rushing. Again, the Chargers block this one straight. The mistake is made by a (severely hobbled) D.J. Fluker. Fluker's responsibility is to pick up DT Tom Johnson while Woodhead comes in front of Rivers and picks up whomever Watt doesn't. Instead, Fluker doubles with Watt on LB Anthony Barr, leaving Woodhead with no one to block and giving Johnson a free run at Rivers.
"Teams run quick screens, slants, things like that, because normal pass routes take too long and the pressure is right on the quarterback."-Jeremiah Trotter in Blood, Sweat and Chalk, Page 229.