Bumping this to the front page in case you missed it...
Most people seem to be quite optimistic indeed about the prospects for the Stanford defense in 2012. We've heard people including the Stanford linebackers in the discussion of "best unit in the conference" up there with USC WRs and such and the front 7 as one of the best of the country. So it'd seem reasonable to ask--well, you've seen the headline.
Start by establishing the baseline--how good were the defenses that preceded the upcoming one? Table (conference rank in parentheses):
|Year||Points per game allowed||Yards per play allowed|
|2009||26.5 (8th)||6.0 (8th)|
|2010||17.4 (1st)||5.1 (5th)|
|2011||21.9 (2nd)||5.45 (5th)|
While the absolute stats in 2011 look worse than 2010, it looks similar when compared to its conference peers. That's probably due to the number of high-powered offenses in the Pac-12; when you add to that the distorting effects of bowl games (who'd you rather face, defensively, in your BCS bowl: Oklahoma State or Virginia Tech? This question will not be scored in the exam.) Nevertheless, the backsliding from 2010 in 2011 is not exactly reassuring; the defense will not have such a highpowered offense to rely upon. Was it pass defense or run defense that's responsible for the decline? Let's adjust the stats by keeping in mind that the NCAA is incredibly foolish by counting sacks as run defense rather than pass defense. Once you adjust, here's how the two teams stack up against the two types of offensive plays:
|Year||Yards per pass||Yards per run|
|2010||5.18 (3rd)||4.89 (5th)|
|2011||6.1 (4th)||3.59 (2nd)|
As I'm sure precisely no one is shocked to hear, the defense against the pass declined quite a bit--turns out, losing your best cover corner to the NFL tends to hurt; losing your safety to injury for large parts of the season and being forced to rely upon a true freshman and a walk-on as depth tends to hurt quite a bit too. If there's anything that's a consolation, it's that sacks played a huge role in the defense in 2011--without sacks, Stanford would've been a mediocre 6th in the conference against the pass on a per play basis.
The strengths of the 2011 defense can thus be reasonably projected into 2012--the team is only losing 5 out of its 39 sacks; that loss can easily be replaced by Shayne Skov plus improvement from other players. It's reasonable, actually, to hope for the 2012 sacks total to push into the forties. The run defense and tackles for loss can be projected along the same lines.
What about the weaknesses? There were two big ones in 2010--inexperience and pass defense. Let's take a look at inexperience first. Here's the percentage of players in each years' depth chart from 2009 who are upperclassmen (season-ending unless otherwise noted. For the 2012 depth chart, we're going to use Wilner's reconstructed spring game depth chart.)
Note that the 2012 depth chart doesn't include Shayne Skov. That said, the 2012 number is probably deceptive--the only way for underclassmen to get on the two-deep is if they're sophomores; no freshmen are on the team yet. Nevertheless the number reflects that there's quite a few returning players from a fairly good defense in 2011 and that any true freshmen getting playing time in 2012 is really good indeed.
That only leaves the defensive back question. Experience here is an issue yet again. 6 of 9 defensive backs on the depth chart were upperclassmen in 2010 and that number dipped to 4 of 9 in 2011. When you consider the injury issues of Delano Howell, perhaps even that number deserves a bit of an asterisk. That number holds steady in our (projected) spring depth chart with 4 of 9; if there's something to be optimistic about, one of those upperclassmen won't be the oft-targeted Johnson Bademosi. If there's something to not be so optimistic about, the safeties are not exactly reassuring--there might be a large shortfall from Thomas/Howell to whomever ends up replacing the pair. For one last bit of optimism: the level of talent as measured by recruiting gurus has likely never been higher. There will be four players in the secondary who were assessed to be four-stars by one of the major four services in 2011. That compares to zero in 2009, one in 2010, and three in 2011. The theoretical talent base is rising in the secondary. (It's also rising in the front seven and even more dramatically--but you weren't worried about that, now were you?)
So this just confirms what you thought anyway: the defense projects to be really good indeed next year. But you should be comforted that the numbers are on your side. Allowing 18 or 19 points per game in 2012 seems like a reasonable goal.
(I'm pretty sure I've counted everything right--but if you think I've got something wrong...I probably haven't.)