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Why The 2015 Cowboys Defense Was Not As Bad As You're Being Told

The Aikman Efficiency Rating suggests the 2015 Cowboys' defense may have been a lot better than most people are giving it credit for. Are you buying it?

Jerome Miron-USA TODAY Sports

For months, the nattering nabobs of negativism have been wallowing in the ineptitude of the 2015 defense and have been throwing around a few key stats to prove their point:

Just 31 sacks (ranked 26th)
Only eight interceptions (ranked 31st)
A meager three fumble recoveries (32nd in the league)

The best thing about those numbers is that they can be used to endlessly rain on the 2016 Cowboys parade! How can a team that's missing two of its best edge rushers for four games even dream of getting more than 31 sacks? How can a team that's returning stone-hands Carr and draft-bust Claiborne get any interceptions at all? And with no middle linebacker, forget about those fumble recoveries as well. In fact, forget about the entire dumpster fire that's the woefully under-manned, under-talented and over-self-medicated Cowboys defense.

Fortunately, not everything is that black and white, even if some would have you believe that. So it was with great delight that I re-read an article by Tom Cowlishaw of the Dallas Morning News from a couple of years ago, which explained what stats Rod Marinelli uses to assess his defense. Turns out, the Cowboys use a much more holistic approach to evaluate their defense:

When I talked to Rod Marinelli in training camp, he said there were only two sets of numbers he cared about for his defense: the Aikman ratings and turnovers.

The Aikman Efficiency Ratings were devised by - you guessed it - Troy Aikman, who was looking for a better way to rate offenses than the NFL’s "official" method of measuring offensive and defensive performance: yards gained or allowed. In 2006, together with Rick Odioso, a statistician for Fox Sports and Jim Henzler, a senior analyst for Stats Inc., Aikman created the formula for the Aikman Efficiency Rating (AER), which combines seven stats in five categories that Aikman and his cohorts believed offered a truer picture of offensive and defensive strength.

The exact formula used to arrive at the ratings was never made public, and remains proprietary to Stats Inc., but we do know what the seven stats are that go into the metric and how they are weighted in the metric:

Metric Weight Detail
Adjusted Points 20% Total points scored or allowed minus points on returns and safeties
Turnovers 20% Turnovers allowed on offense or turnovers generated on defense
Red Zone Efficiency 20% Percent of possible points - Number of points scored on red zone opportunities divided by total red zone opportunities multiplied by seven
Yards Per Play 20% 10% - Yards per rush attempt
10% - Yards per pass attempt including yards on plays involving sacks.
First Down Achievement 20% 10% - Number of 1st downs gained or allowed
10% - 3rd down conversion percentage

While we don't know how the Aikman Efficiency Ratings are ultimately calculated, we do know that the stats above are combined into one single number and then adjusted against a league norm established over the last 10 years.

The resulting number ranges from somewhere around 50 up to a maximum of 100, and the better the offense or defense, the higher the score on either scale. The average on offense is around 80 points, the average on defense is slightly below 70 points. Combine the two numbers and you get a value for overall team efficiency.

But before we walk through the individual stats above for the 2015 defense, let's first look at how the 2015 defense compared to the 2014 defense in its overall ranking:

Dallas Cowboys
2014 Defense
2015 Defense
Aikman Efficiency Rating 69.6 67.0
NFL Rank 15th 17th

Going by the numbers here it's pretty clear that the 2015 Cowboys defense was just as good (or bad) as the 2014 defense. You've ben told otherwise, you may even believe otherwise, but the metric the Cowboys use to evaluate their defense speaks a clear language.

Before you put this off as another set of esoteric stats in a public display of ignorance ("Hey, did you know that the team that scores more points wins 100% of the time"), consider that Rod Marinelli isn't the only coach who likes the Aikman Ratings.

"We're No. 1 in the Aikman ratings, which takes all of the important statistical categories into consideration," Chicago head coach Lovie Smith said in 2012. "I'm pleased with third downs, takeaways, scoring, playing the run; all of those things."

But how can a 2014 defense that ranked second overall with 31 takeaways be even remotely comparable to a 2015 defense that ranked dead last in the league with 8 takeaways? The simple answer is that defense is about more than just takeaways (though they help a heck of a lot). The more complex answer is that there are a bunch of key metrics that determine the overall performance of a defense, and the Aikman Rating captures some of the most important ones.

So let's walk through the different stats that make up the Aikman Rating and see how the two defenses differed.

Adjusted Points: The Cowboys allowed 374 points last year. According to Pro-Football-Reference.com, four interceptions were returned for a TD, along with a kick return and a fumble return for a total of six return TDs worth 42 points. The remaining 332 Adjusted Points rank the Cowboys 15th in the league, exactly where they were ranked in 2014 as well.

Red Zone Efficiency. The Cowboys' 2015 opponents had 49 red zone possessions. At seven points per possession, those opponents could have scored 343 points, but only scored 221 for an efficiency percentage of 64.4%, the 7th best value in the league. In 2014, the Cowboys defense had an efficiency percentage of just 70.6%, ranked 23rd in the league. Clear advantage for the 2015 defense

Yards per play: The 2015 Cowboys allowed 4.2 yards per attempt on the ground (20th) and 7.6 yards per attempt through the air (24th). In 2014, they were ranked 19th on the ground, also with 4.2 Y/A, and 21st through the air with 7.5 Y/A. No significant differences between the two defenses.

First down achievement.

  • The Cowboys allowed 317 first downs last year, the 14th best value in the league and a slight improvement over their 17th rank from the year before
  • Last year, they were ranked 15th with a 38.9% third down conversion percentage allowed, a significant improvement over their 43.6% percentage from 2014 (27th).

Turnovers: As already mentioned, the Cowboys fell from second overall with 31 takeaways in 2014 to dead last in the league with 8 takeaways.

In summary, the 2015 defense was better in the red zone and on 3rd downs, while dropping off spectacularly in takeaways. In the Aikman Rating formula all of that ultimately balances out, and the metric suggests that the Cowboys had average defenses in both 2014 and 2015. No more, but also no less.

Compare that to the numbers for the Cowboys offense and the difference is much clearer.

Dallas Cowboys
2014 Offense
2015 Offense
Aikman Efficiency Rating 90.9 73.7
NFL Rank 3rd 29th

The Cowboys offense, provided its key players stay healthy, is widely expected to bounce back to somewhere close to the level it played at in 2014.

The defense on the other hand is widely projected to rank near the bottom of the league. I believe that is wrong. I believe the defense will rank in the top half of the league.

Despite the dramatic drop in turnovers vs 2014, the defense improved in other key metrics in 2015. And takeaways, like all variables that are extreme on their first measurement will tend to be closer to the average on a second measurement. There's a very good probability that the Cowboys will generate more takeaways in 2016 than they did in 2015, and coupled with improved play in the red zone and on 3rd down, that will see the Cowboys defense move up from its middling rank in 2015 to a better rank in 2016.

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