I was initially stumped back in April when Seattle elected to blow a second straight late draft on defensive backs. CB Richard Sherman, FS Mark Legree, CB Byron Maxwell all became Seahawks, even as defensive tackle remained a gaping wound on the defense. It looked as if Carroll and Schneider's priorities were backwards. Secondary before pass rush? That's not how it works. Let the QB stand in the pocket for long enough, and even the best secondary will be exposed. QB pressure, on the other hand, helps that secondary.
However, it can also work the other way around. No matter how quick off the snap your defensive line is, it's going to take them at least a couple seconds to reach the QB. Offenses have developed the quick-rhythm passing game to exploit those first seconds - getting the ball out before pressure arrives. It depends on receivers being able to get a clean release off the line of scrimmage and quickly flash open.
So those first couple seconds are part of the game as well. The most obvious solution: jam the receivers right off the snap. Throw off their timing and the QB has a harder time dumping the ball off, giving pass rushers more time.
So I believe it's true that the secondary can help the pass rush in the opening moments of a play, after which the D-line has to do its job or the secondary will be exposed downfield. Overall, the responsibility of stopping a QB has been said to fall 75% on the pass rush, 25% on the secondary.
As I look at the "big, strong press guys" theme of this secondary, it looks like Carroll is trying to attend to the secondary's 25%. His press coverage, or "bump and run" is meant to disrupt receivers at the line. He wants his corners to play to the inside of the receiver to take away the big seam plays and force receivers to the outside, where the QB has a tougher throw. This requires cornerbacks with both strength and physicality at the line, and speed and fluidity to transition from jamming to running. That's not a common combination, and the more height you have, the rarer it actually gets.
A CB can't play press coverage if you don't have guys who can both jolt a receiver and recover from failed jams to run with him. Put simply, the ideal bump-and-run CB has to be able to both bump and run. And tall CB's tend to lack the hip fluidity and speed to do both, which we're seeing a lot of on the roster. This dictates your scheme. If you can't run, you rely on your jams and get burned deep if they fail. If you can't bump, the receivers are free to streak downfield, requiring corners to start deep and limit the damage - bigger cushions.
The better option, and Carroll's stated preference if you can't both bump and run, is to abandon the bump. This means frustrating cushions and more easy completions, which fits what we saw last year. This is one genesis of bend-but-don't-break - it's not necessarily an intentional choice, but a compromised forced by limited tools at cornerback (and other positions).
It's likely to remain that way until Carroll is able to address the position in the draft and stop settling for dumpster-diving. Thurmond could be the answer at #2, but he's almost behind the curve now.
I'm pretty cool toward this CB corps. They're just so uniformly young, with no appreciable NFL experience back there. Every big play they make in camp is tempered by the fact that the passes are coming from Tarvaris Jackson, Charlie Whitehurst, and Josh Portis. By the time Seattle's bye rolls around, they'll be coming from Ben Roethlisberger, Matt Ryan, and Eli Manning. (That's another manner in which a bad QB situation affects your team: it doesn't try your defense in practices.)
So here's to hoping that someone on this young team can defy their scouting reports and flash the press skills they need.