The long, slow march through the offseason continues today with a statistical query inspired by Texas' dichotomous run-pass defensive splits in 2006.
Texas finished the 2006 season ranked third nationally in rush yards allowed per game (62.1). They also finished the season ranked 99th in pass yards allowed (236.2). In trying to wrap my mind around how big a difference that really is, I decided to dig through last year's stats to see how anomalous Texas' performance was.
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Take a look at the following chart, which lists the top 40 teams in rush yards allowed per game side by side with their pass yards allowed per game rank, as well as the delta. Teams with deltas greater than 60 are highlighted in yellow.
The data scatterplotted:
When I looked at these numbers, I immediately knew something was wrong. Take Michigan, for example, a team I watched frequently last season. Unable to run the ball even a little bit on the Wolverines, opposing offenses simply took to the air.
But what about the rest of the teams on the list? I suspected that this data was misleading, but I couldn't rule out the possibility that strong rush defense teams are simply more vulnerable to the pass. I decided to chart the top 40 ranked rushing teams by pass yards allowed per attempt
As suspected, the rankings for many of the teams improve dramatically. Michigan improves from 89th in total pass yards allowed to 20th in pass yards per attempt. Big improvements also for Florida, Penn State, UCLA, USC, Florida State, Ohio State, Oklahoma, Georgia Tech, Louisville, Wake Forest, SMU, Kansas, Boston College, BYU, Arkansas, Nebraska and New Mexico. Many more were ranked mildly better.
Only a few teams, though, were poor both in total pass yards allowed and in pass yards per attempt. And Texas was one of those teams. Even adjusting the data to control for the number of times opponents threw against the Longhorns, Texas still ranked 86th nationally.
Of the top 40 teams, only nine (West Virginia, Utah, SMU, Colorado, Washington State, Mississippi State, Navy, Arizona State, and New Mexico) joined Texas as below average (ranked 60th or worse) in pass yards allowed per attempt. Only three (West Virginia, Washington State, and Mississippi State) were outside the top 80. On a normal distribution, you'd expect six or seven teams to fall below that threshold, which suggests that these four teams were unsually inept at defending the pass in 2007.
Just looking at the numbers, we can't explain why Texas was so bad in pass defense; for that, we'd need to actually chart plays, re-watch the games, and scout mistakes. One thing's pretty clear, though: the Texas pass defense in 2007 - despite losing three starters in the secondary - can't be much worse statistically than the 2006 team.