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Back in early April last year, before the draft, I wrote an article titled "Cowboys Key To Success in 2012 Is Improved Passer Rating Differential." The Cowboys had just come off an 8-8 season in 2011, and while they were ranked fourth overall as a passing offense (100.1 offensive passer rating) they were ranked a lowly 25th as a passing defense (88.4 defensive passer rating). In 2011, the Cowboys had combined one of the most efficient passing attacks in the league (and the most efficient in franchise history as measured by passer rating) with a very poor pass defense.
The difference between the offensive passer rating and the defensive passer rating is called the passer rating differential. Despite their paltry 8-8 record in 2011, the Cowboys ranked a respectable ninth overall in passer rating differential (+11.7), and I argued at the time that the quickest way to get more wins for the Cowboys in 2012 was to improve the passer rating differential. And since there wasn't much room for improving the passer rating differential via the offense, that left the defense as the main area to focus on. The Cowboys had already signed Brandon Carr in free agency, and when they drafted Morris Claiborne a few weeks later, I felt reasonably optimistic about the Cowboys pass defense heading into the 2012 season, especially since the 2012 season showed once again how dominant the passing game has become in the NFL:
- There were a record-breaking 126 individual 300-yard passing performances in 2012. The previous two records were 121 in 2011 and 104 in 2009.
- There were 15 individual 400-yard games in 2012, slightly below the 2011 record of 18, but ahead of the previous record of 14 set in 2004 and 1986.
- In the last two years, seven quarterbacks have passed for more than 4,900 yards: in 2011, Drew Brees, Tom Brady, Matthew Stafford and Eli Manning passed that mark, in 2012 Brees and Stafford repeated while Tony Romo joined their ranks. Prior to the last two seasons, there were just two QBs in the entire history of the NFL who surpassed that mark (Dan Marino, 5,084 in 1984 and Drew Brees, 5,069 in 2008).
As it turns out, the Cowboys were not particularly successful in 2012, and their passer rating differential is a key reason for that: In 2012 the Cowboys combined an above average passing offense (91.3 passer rating, ranked ninth in the league) with an atrocious pass defense (94.7 defensive passer rating) that ended up 29th in the league. The resulting passer rating differential of -3.4 ranks 18th in the NFL.
Proponents of volume stats would argue that the Cowboys "only" gave up 3,684 passing yards, an average value which ranks them 19th in the NFL, and that "atrocious" is not the right word to describe the Cowboys pass defense. Those people couldn't be more wrong. The number of yards you accumulate or give up has almost no correlation to winning or losing in the NFL, as we'll see a little further below.
Today, winning in the NFL is all about passing efficiency. The best offenses are those that pass the ball the most effectively, the best defenses are those that prevent their opponents from passing effectively. The best teams in the league are those that do both most effectively.
Here are the 2012 teams as ranked by passer rating differential:
| Passer Rating Differential, 2012 |
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| Rank | Team | PR Offense | PR Defense | PR Differential | Rank | Team | PR Offense | PR Defense | PR Differential |
| 1 | Green Bay | 108.3 | 76.8 | 31.5 | 17 | Buffalo | 82.2 | 84.4 | -2.2 |
| 2 | Seattle | 100.6 | 71.8 | 28.8 | 18 | Dallas | 91.3 | 94.7 | -3.4 |
| 3 | Denver | 105.3 | 79.4 | 25.9 | 19 | Carolina | 86.5 | 91.7 | -5.2 |
| 4 | San Francisco | 101.2 | 78 | 23.2 | 20 | Miami | 76.7 | 83.4 | -6.7 |
| 5 | Atlanta | 99.1 | 77.1 | 22.0 | 21 | Arizona | 63.1 | 71.2 | -8.1 |
| 6 | Washington | 102.1 | 87 | 15.1 | 22 | NY Jets | 68.3 | 78.2 | -9.9 |
| 7 | New England | 97.7 | 86.9 | 10.8 | 23 | Detroit | 81.5 | 91.7 | -10.2 |
| 8 | Houston | 89.2 | 80 | 9.2 | 24 | Minnesota | 81.2 | 92.3 | -11.1 |
| 9 | Chicago | 80.4 | 71.3 | 9.1 | 25 | Tampa Bay | 81.8 | 93.5 | -11.7 |
| 10 | Pittsburgh | 88.1 | 79 | 9.1 | 26 | Cleveland | 73.5 | 86.6 | -13.1 |
| 11 | Cincinnati | 88.1 | 80.7 | 7.4 | 27 | Indianapolis | 76.4 | 90.1 | -13.7 |
| 12 | Baltimore | 86.4 | 80.6 | 5.8 | 28 | Jacksonville | 74.7 | 89.8 | -15.1 |
| 13 | New Orleans | 96.4 | 93.8 | 2.6 | 29 | Oakland | 82.4 | 97.5 | -15.1 |
| 14 | San Diego | 88.5 | 87.9 | 0.6 | 30 | Tennessee | 76.9 | 92.7 | -15.8 |
| 15 | St. Louis | 82.7 | 83.9 | -1.2 | 31 | Philadelphia | 78.6 | 99.6 | -21.0 |
| 16 | NY Giants | 87.2 | 88.7 | -1.5 | 32 | Kansas City | 63.8 | 99.9 | -36.1 |
| Playoff teams highlighted in bold | |||||||||
10 of the top 12 teams in this metric made the playoffs this year. Much to my statistical displeasure, the Vikings and Colts stick out like two sore thumbs in this table. Both are fundamentally flawed teams in terms of passer rating differential, but both found ways to overcome those flaws and make the playoffs.
In statistics, the relationship between two variables is called a correlation, and the strength of that correlation is measured by the "correlation coefficient". This coefficient (r²) is expressed as a number between 1 and -1. The closer the r² number is to 1 or -1, the stronger the relationship between the two variables. The closer it is to zero, the weaker the relationship. R² between Passer Rating Differential (PRD) and wins in 2012 was 0.65. At first glance, that doesn't appear to be that high of a value. But if we were to exclude the Vikings and the Colts, that correlation would jump to 0.80, the long term average for this metric in the NFL. Here's a graph that illustrates the correlation between Passer Rating Differential and wins for all 32 NFL teams in 2012:
The two outliers notwithstanding, the graph illustrates fairly clearly that there was a strong link between wins and passer rating differential in 2012.
And while we're calculating correlations, here's how some other frequently and less frequently used stats correlated with wins in 2012:
| Stat | R², 2012 |
| Points Differential | 0.84 |
| Passer Rating Differential | 0.65 |
| ANY/A* Differential | 0.65 |
| Net DSR* | 0.64 |
| Points For | 0.64 |
| Passer Rating Offense | 0.53 |
| Points Against | 0.53 |
| NY/A* Differential | 0.52 |
| Y/A* Differential | 0.46 |
| Turnover Differential | 0.45 |
| Passer Rating Defense | 0.29 |
| Passing Yards Offense | 0.06 |
| Passing Yards Defense | 0.01 |
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*ANY/A: Adjusted net passing yards per attempt = (Passing Yards + (Passing TDs)*20 - (INTs thrown)*45 - Sack Yards) / (Passing Attempts + Sacks) *NET DSR: Drive Success Rate measures the percentage of down series that result in a first down or touchdown = (First Downs + Touchdowns) / (First Downs + Drives) *Y/A: Yards gained per pass attempt (Passing Yards / Passes Attempted). *NY/A: Net yards gained per pass attempt, which is basically Y/A adjusted for sacks (Passing Yards - Sack Yards) / (Passes Attempted + Sacks).
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Passer rating differential beats almost any other available stats in terms of how closely it correlates to wins in the NFL. It follows that as a team, you should do everything you can to improve your passer rating differential, no?
Back to the Cowboys. We've established once more that passer rating differential is one of the stats most closely linked to winning in the NFL. It stands to reason that if the Cowboys want to make the playoffs next year, they'll have to improve their pass defense. And it's not just a question of waiting until the injured players on defense return to health. Here's a breakdown of the Cowboys' defensive passer rating by weeks:
- Weeks 1-6: 97.7 - The Cowboys still had Sean Lee and Bruce Carter, and the only significant injury was Barry Church, who tore his Achilles tendon in Week 3. So even with a relatively healthy defense, the Cowboys pass defense didn't look good. At all.
- Weeks 7-11: 85.6 - Sean Lee was injured in the Week 7 game, but the Cowboys still had Carter and Scandrick patrolling the middle of the field, as well as Ratliff returning during this period. Some improvement in the Defensive Passer Rating but only to a level marginally better than the 88.4 rating the pass defense had in 2011.
- Weeks 12-17: 100.6 - Scandrick, Carter, Ratliff are all out for the season and injuries keep mounting at other positions as well. The pass defense reverts to the level of the first couple of weeks.
The Cowboys brought in a new secondary coach and two shiny new corners, yet the pass defense regressed to a level below even that of the 2011 defense. And as we can see above, injuries alone are not the explanation, as the Cowboys didn't play any better when healthy.
When you're looking to improve your pass defense, you have basically two areas that you can focus on, the secondary or the pass rush. With what the Cowboys have already invested in the secondary, coupled with the fact that the Cowboys' sack total of 34 is the lowest since 2006, improving the pass rush could very well be the Cowboys' top offseason priority.
At the end of the day, if the Cowboys want to succeed in 2013, they'll have to fix their passer rating differential. How they go about that, via an improved pass rush, improved secondary or perhaps even an improved offense, is largely a philosophical question.