After careful consideration I've concluded that John Fox knows more about football than I do. I was expecting us to draft Marcel Dareus and maybe another defensive tackle or two. To my dismay we got Von Miller and some other nice prospects but no defensive tackles. Then I saw a table — can somebody tell me who posted it, so I can give credit? — suggesting that teams with dominant running attacks don't win nearly as consistently as teams with dominant passing attacks. I suspect the obverse is also true, that if a team can only do one or the other it's better to have a dominant pass defense than a dominant run defense. And with that thought I began to get a glimmer of what Fox has been up to.
In 2010 we gave up 471 points, ranking 32nd, and ranked 32nd in rushing TDs given up, 31st in rushing yards allowed and 29th in yards per carry. With mediocrity seemingly permanently entrenched at defensive tackle it seemed obvious our first pick would be either Dareus or Fairley. But was rushing defense really our achilles heel? After all our run defense was almost as bad in 2009, at 4.5 vs 4.7 ypc, yet we gave up only 324 points, ranking a respectable 12th. The difference was pass defense. In 2010 we allowed 7.2 net yards per attempt*, ranking 30th, whereas in 2009 we allowed only 5.4, ranking 3rd. That's a huge difference. I don't think our secondary declined that much in one year. It was arguably pressure that made the difference. In 2009 Dumervil had 17 sacks and the rest of the team 22 for a total of 39, ranking a very respectable 10th. But in 2010 an injured Dumervil had none and everybody else 23, which ranked dead last. Interceptions showed a similar pattern. In 2009 Denver had 17, tied for 13th, but in 2010 only 10, ranking 31st. Clearly the decline in pass defense effectiveness was drastic, but does a difference of seven interceptions really account for a 147 point swing?
To understand why effective pass defense even with a relatively ineffective run defense can make such a large difference we need to understand how passing and running interact, and why passing is nonetheless arguably more important. Discontinuity is the enemy of offense. Teams very rarely score or move into scoring position from their own side of the 50 on a single running play, and not that often on pass plays. We hardly ever see TD drives in which no first downs are made. To score teams ordinarily have to convert several third downs, and a majority won't do. A single failure to convert will stop the drive. At first glance it might appear that against a really poor run defense the opposing team can simply run the ball over and over, getting first down after first down, until finally plowing into the end zone. Observant fans know, however, that even a poor run defense will from time to time stop a run for little or no gain. It's not frequent but not extremely rare, either. It's the 7 to 15 yard runs that up the average. That means that for even a poor run defense, and more often for a solid one, the other team will during the game face a number of third and medium or third and long situations. If the defense can't pressure the QB an unacceptably high percentage of these downs will be converted and fans will see a defense that can't get off the field.
That doesn't mean the run game is irrelevant. A running game that rarely gets stuffed tends to keep second and third downs at manageable distances, and if it can consistently pick up third and short on the ground that, too, is an aid to the offense's continuity. Hence from the defense's perspective stopping third and short, stopping the runner for no gain or a loss on first or second down, and preventing completions on third and medium or long are all important and all depend on the same basic attribute: getting penetration. Fox and Allen have made it clear that they want a disruptive defense, not just a sideline to sideline wall, and disruption is usually, directly or indirectly, caused by penetration. It leads to tackles for a loss, sacks, interceptions and fumbles. Fox's coaching and personnel moves, starting with Miller, are apparently predicated on disruptiveness in general (Moore knocking receivers silly, for instance) and penetration.
It's clear to me now that Fox's priority all along, regardless of what we thought, was to create a blistering pass rush, the quickest route to improvement on the scoreboard. Having Dumervil back and taking the most explosive player in the draft bids fair to turn a weakness into an overwhelming strength, thus maximizing the team's ability to keep opponents from scoring. It seems to be working. Denver's starters have outscored their counterparts on Buffalo and Seattle 14-3 and 17-3. Looks like this Fox knows what he's doing.
*Passing yards minus yards lost in sacks divided by passing attempts plus sacks. Stats taken from Pro-Football-Reference.com except for totals and rankings for sacks and interceptions, taken from ESPN.