Below you will find a listing of statistics put up by the Dallas Cowboys defense in 2015.
Yards per play: 19th
3rd down%: 18th
Redzone scoring %: 8th
Rushing yards: 22nd
Yards per rush: 19th
Yards per pass: 23rd
Passer rating against: 20th
The first thing I'd like to call your attention to is that most of these numbers rank in the bottom half of the middle third, which is to say, they are on the low side of NFL average. There seems to be some confusion on this point, as the cries over how bad the defense is going to be are, in some circles, reminiscent of two years ago, when it was going to be worse than "the worst defense in franchise history."
But now let me call your attention to a pretty key stat up there: red zone scoring %. They ranked 8th. And surely that is an important stat. In fact, in points per game, the team is squarely in the middle at 16th and, after all, isn't preventing scoring what defenses are all about? The Dallas defense gave up 306 points (only counting scores at the end of drives and ignoring extra points) on 166 drives for 1.84 points per drive, a stat suggested by former front page writer Neithan20000 to measure the effectiveness of a defense. The NFL as a whole (including the Cowboys) gave up 9804 points on 5,702 drives, or about 1.71 points per drive. Once again Dallas comes in just below average. For comparison, the Buffalo Bills ranked 15th in overall scoring defense giving up 306 points in 179 drives for roughly the same 1.71 points per drive (the un-rounded numbers are slightly different), so this near-middle ranking does seem appropriate.
Neithan20000 also suggested a statistic for measuring explosiveness of an offense -- points per play. The NFL at large took 33,339 plays to score their points, for a 0.29 point per play average. Dallas' opponents took 1,001 plays to score their 306 points, for 0.31 points per play. So this "just below average" theme continues. Again, certainly in need of improvement, but hardly the worst defense around.
But that's just the tip of the iceberg. I'm here to explain that there's actually reason to believe the 2015 Dallas defense was quite capable -- far more so than "slightly below average."
In my post regarding how a good, effective offense helps a defense I identified two areas: turnovers (tied to playing with a lead) and time of possession/ plays run in the first half of a game. While the time of possession for the entire game was nearly identical from 2014 to 2015 and the number of plays run was only down by about one per game, there was a significant difference in first half plays run and time of possession. Specifically, the offense in 2014 spent about 1:27 minutes and 3.7 more plays per game on the field in the first half than it did in 2015. While one play a game may not be significant, 3.7 plays a half should be, mathematically speaking, seven times as significant.
The 2014 Dallas defense spent 12:22 first-half minutes on the field per game. The 2015 spent 13:45. The 2014 defense played 26.8 first-half snaps per game. The 2015 defense played 30.7 snaps. Is four plays in a half, on average, enough to cause extra exhaustion? Is 1:23 minutes a significant amount of time? I encourage you to spend 1:30 in a boxing ring or octagon... or failing that, just run wind sprints for that length of time for comparison. Maybe the idea that the Dallas defense wore out is correct and we've just been looking, again, in the wrong place. Being worn out at the end of a game isn't a problem; being worn out in the middle of one is. Do the stats bear out that the Dallas defense performed worse in the second half?
Overall, NFL teams gave up 5.47 yards per play, 1.71 points per drive, and 0.29 points per play in 2015. In the first half of games, they gave up 5.47 yards per play, 1.70 points per drive, and 0.29 points per play. In the second half, they gave up 5.48 yards per play, 1.71 points per drive, and 0.29 points per play. In other words, across the NFL, there was almost no difference in yardage and points per play between the first and second half.
The Cowboys, however, were drastically different. They gave up 5.0 yards per play in the first half. For reference, 5.0 yards per play is how the top five defenses in yards per play performed. Carolina and Seattle came in at 4.9, the New York Jets and Houston at 5.0. Only Denver at 4.4 was significantly better. In the second half for Dallas, that number ballooned to 6.1 yards per play, which ties with the Cleveland Browns and New York Giants for 30th and only the New Orleans Saints faring worse. That's a pretty drastic swing.
The pass defense also showed a massive shift. 86.0 passer rating with 6.5 yards per attempt in the first half, 103.4 passer rating and 8.9 yards per attempt in the second. A 2.4 yard per attempt difference is silly. For perspective, 8.9 yards per attempt is 1971 Roger Staubach. 6.5 yards per attempt is 2011 Josh Freeman or 2012 Brandon Weeden. A 103.4 passer rating is 1976 Ken Stabler, 86.0 is Jay Cutler's last year in Denver (2008).
Scoring-wise it was truly ugly in the second half, as the healthy 0.27 points per play for Dallas swooped to a scary 0.34 points per play, indicating offenses were about 25% more explosive. Per drive, the numbers echo these sentiments, with first-half points per drive against coming in at a much-better-than NFL average 1.55 and the second-half tipping the scales at a rancid 2.15 -- showing a nearly 40% increase in the productivity of opposing offenses.
The Dallas defense was a Jekyll-and-Hyde affair, playing like champions in the first half of games and horrifically in the second halves. You weren't imagining the collapses.
But even overall, you who remember a relatively effective Dallas defense, weren't imaging it either. If you take punts forced, the Dallas defense was tied for 8th with the Rams, Ravens, and Bears at 44%. In terms of giving up touchdowns, they were overall tied for 15th with the Chargers, Bills, and Ravens - once again, right in the middle. Here's where the turnover deficit really hurt, as the inability to get turnovers greatly impacted what was otherwise a very good stop rate. And this can be tied directly to the inability of the offense to take the lead.
You see, the Dallas defense under Marinelli, and Kiffen before him, has a very distinct pattern. All three years, 2013, 2014, and 2015, individually; drives that result in turnovers start out five points further behind, on average, than drives which do not. The actual score differential varies, but the difference in turnover-drives and non-turnover drives was very consistent: 4.9, 4.9, and 5.1 points. How much of a chance did the defense give the offense to take a lead?
In the first half, the 2015 Dallas Cowboys forced punts on 54% of drives, second only to the Seattle Seahawks at 56%. They gave up touchdowns on a mere 18% of drives, tied with the Green Bay Packers for 9th. That's stout play. That's playoff caliber play. They just couldn't sustain it. And they couldn't get turnovers to help them in the second half. The 2014 Cowboys feasted in the second half of games, averaging about 1.4 second half takeaways a game. In 2015, they got less than half a one per game. And the result is there for all to see: their touchdown percentage swelled to 26%, tied for 25th in the league and their punts forced percentage fell to 33%, tied for 28th. 40% less effective at getting stops and with opposing offenses nearly 50% more effective at getting touchdowns. But the turnovers are really the key.
Funny thing: if you sort the overall drive stats by turnover percentage, the first 13 teams were playing with leads. The bottom seven were all playing at a deficit. Offense helps.
And a mere league average number of turnovers would vault the team forward in the scoring rankings. You see, for all the good above, the Cowboys gave up scores of some sort on 40% of their drives, putting them in the bottom third of the NFL. Adding in the league average for turnovers places them at 33%, tied for 11th with the Rams and one spot behind the Seahawks.
And here again, the halves of the game show themselves. Dallas gave up scores on 34% of first-half drives, tied with the Cardinals for 11th. In the second half, they gave up scores at a ridiculous 46% rate, ahead of only the Browns and Saints.
Yet, despite all the positives in the first-half play, the team has, in fact, made improvements... beyond adding Ezekiel Elliott. If I were to ask the two weakest points on the 2015 Cowboys defense, nearly everyone would say Nick Hayden and J.J. Wilcox. Hayden is gone, replaced by the highest-paid free agent the team signed, Cedric Thornton, and Wilcox has had first-round pick Byron Jones placed squarely on his six o'clock. Furthermore, safety Barry Church had two similar players signed (in an almost personal fashion) and Rolando McClain has been given a warning shot as well, with the team investing a high-round pick on an injured middle linebacker who has a reputation for his desire to play. Two more relatively high draft picks (67 and 101) look to add depth to the defensive line.
All this to say, the 2015 Cowboy defense was, in fact, capable of very good play, and the team has clearly addressed its biggest weaknesses. If you are thinking the defense will come in and usher the other teams into the Dallas end zone, you may have another thing coming.
Here are links to the raw, sortable drive data, the first-half drive data, and the second-half drive data.