Say what you want about special teams, but Stanford’s pass defense cost it the Fiesta Bowl.
On that fateful night in January, the Cardinal executed its game plan to perfection in the three other phases of the game: it rushed for 243 yards and three touchdowns, allowed practically nothing from Oklahoma State on the ground and benefited from a 27-for-31, 347-yard effort from Andrew Luck in his final collegiate game. But with Cowboys quarterback Brandon Weeden throwing for 399 yards of his own, Stanford couldn’t close things out the way it would have wanted to, and Oklahoma State came out on top in overtime.
So as the Cardinal opened its fall training camp Sunday without the three graduated members of its 2011 starting secondary, it makes sense that pass defense would be the squad’s greatest concern after the quarterback position. Defense wins championships, of course.
But as it turns out, to succeed in the best passing conference in the nation, the strength a Pac-12 defense needs the least is…an airtight secondary.
This conclusion, counterintuitive as it may seem, is made readily apparent by studying the correlation between the defensive stats of each Pac-12 team and how many games the individual teams won for a single season. For the non-stats majors in the crowd, correlation (with a magnitude ranging from zero to one) is a simple measure of the interrelatedness of two variables. A perfect correlation of one indicates that, when these data points are plotted, they form a perfectly straight line; a correlation close to zero means that the data points are spread randomly. For example, you would expect a pretty high correlation between a team’s wins and the number of points it scores, but a much lower correlation between its wins and, say, the number of fair catches it records.
Since allowing fewer passing or rushing yards is a good thing, the correlation between either of these stats and wins is expected to be negative, but keep in mind that it’s the magnitude that counts here. A comparison of these correlations is a strong indicator of which is more “important” to a team’s success—essentially, whether a solid secondary should be valued over a formidable front seven or vice versa.
Take 2011. Believe it or not, in a season full of pass-happy offenses led by top-rate quarterbacks—Andrew Luck, Matt Barkley, Nick Foles, Brock Osweiler and Keith Price, to name a few—there was only a correlation of -0.07 between the number of passing yards allowed per game by Pac-12 teams and how many wins they recorded. This figure emerges from the fact that none of the conference’s 10-win teams had a top-five secondary (in terms of yards allowed through the air), and the best pass-stopper in the Pac-12, Cal, finished a mediocre 7-6.
The number of yards allowed per game on the ground, on the other hand, was a much more accurate predictor of how many victories a team recorded, as demonstrated by the -0.80 correlation between wins and rushing defense in 2011. Twelve-win Oregon, 11-win Stanford and 10-win USC finished 5-1-2 in this regard, and no bowl-eligible team in the top five in rushing yards allowed failed to qualify for the postseason last year.
The 2011 season was no fluke, either. In each of the past five seasons, the correlation between rush defense and wins has been stronger than that between pass defense and wins; since 2007, when the two measures were nearly the same, the rush defense mark has never risen above -0.69 and the pass defense mark has never slipped below -0.29. (Remember, larger negatives indicate a stronger relation in this case.) The same general trend repeats itself in terms of just Pac-12 records.
Over that same five-year span, top-three finishers in the Pac-12 average the third-best rush defense in the conference but just the fifth-best pass defense. On the national scale, just one 10-win squad (Arizona in 2007) also finished in the top 10 in Division I for passing yards allowed, but Oregon has reached double-digit wins and boasted a top-10 rush defense for each of the last four years.
There’s an argument to be made that, when comparing front sevens with secondaries, yards allowed are not the only (or even the best) stat to use. A sack or interception can turn the tide of a close game, and bend-but-don’t-break schemes aren’t afraid to give up a few yards on shorter passes—assuming the timely stop comes.
There’s some data to support this assertion: the conference champion has recorded the most sacks in the league three of the last five seasons, and in 2010 the Pac-12’s three top finishers—Oregon, Stanford and USC—recorded the first-, second- and third-most picks, in that order.
But not all big plays are made equal, and again, the front seven reigns supreme. There has been a decent correlation between sacks and wins over the past four years, as this measure has always fallen between 0.51 and 0.72 since 2008. But when it comes to interceptions, things are much less predictable. A 0.71 correlation between picks and wins in 2008 gave way to a mark of essentially zero in 2009, yet in 2010 the correlation was stronger than ever at 0.82. And in 2011, when second-place Stanford had the fewest interceptions (seven) in the Pac-12, the correlation had plummeted back to 0.19.
The moral of the story is that if you’re looking for a playmaker in the Pac-12, a strong pass rusher is a much more reliable bet to improve your team’s fortunes than an electrifying cover guy.
This season you can expect the Cardinal to finish in the top three in the conference in both rushing yards allowed and sacks, and the six Pac-12 teams that have done that in the last five years have averaged 9.67 wins. So while the rest of the world worries about how the Cardinal’s young but talented defensive backs—Wayne Lyons, Terrence Brown, Barry Browning, Devon Carrington, Ed Reynolds and others—will define their roles ins a secondary that had its fair share of struggles last season, I’m just going to sit back and relax while Shayne Skov, Chase Thomas and the rest of Stanford’s dominant front seven do their work.
Don’t forget, I have math on my side.
Joseph Beyda might be teaching an advanced sports statistics course in the fall. Let Professor Beyda know if you’re interested at firstname.lastname@example.org.