LANDOVER, MD - DECEMBER 30: Defensive coordinator Rob Ryan of the Dallas Cowboys looks on in the third quarter of their game against the Washington Redskins at FedExField on December 30, 2012 in Landover, Maryland. (Photo by Rob Carr/Getty Images)
One of the primary reasons we use statistics is to try to garner a superior understanding of reality that our eyes alone cannot provide us. You can watch every throw of Tony Romo’s all season, and it’s highly unlikely you’ll be able to tell me whether he averaged 7.0 YPA or 8.0 YPA without tracking it. There’s a massive difference between those two numbers in regards to the Cowboys’ probable winning percentage, however.
The understanding we acquire from stats is utilized to make accurate predictions. That’s why trivia like “Team X is 23-2 in their last 25 games when they rush the ball at least 30 times” is useless; it’s an explanation of past events, not a predictor of future ones. If it were, teams would make NFL games a race to 30 or more carries.
In this way, some statistics truly are superior to others. Passing YPA has been found to be far superior at predicting future team success than overall passing yards, for example. Similarly, there are defensive stats that “matter” more when trying to predict how a defense will perform in the future. Net-YPA allowed, for example, has proven to be more predictive of future play than rushing YPC allowed.
When we look at the stats posted by the Rob Ryan-led Cowboys defense over the past two seasons, we see that he was actually slightly worse than the traditional stats indicate.
8. Rushing Yards (Rank)
7. Passing Yards
4. Rushing Success Rate
3. Sack Rate
2. Predicted Sack Differential
Above, I listed eight stats, starting with the least predictive. Those at the top are generally used to rank defenses, but they’re usually very poor indicators of future success. On the other hand, stats like net-YPA allowed and sack rate are better indicators of how defenses will perform moving forward.
In terms of rushing yards allowed, the Cowboys’ average rank over Ryan’s tenure was 14.5. In terms of YPC—a better predictor of success—the defense’s average rank was 14. However, the defense’s rank in rushing success rate—the percentage of runs that increase a team’s chances of scoring and the best stat to use when judging rushing ability—was 17. Thus, the defense’s true ability to stop the run during Ryan’s time in Dallas has actually been slightly overrated by traditional stats.
Ryan’s average rank in total passing yards allowed was 21. The Cowboys actually got slightly more pressure than the average team, coming in with an average rank of 13. In terms of net-YPA—the individual stat that’s most predictive of future team success—however, the Cowboys’ mean rank was just 24. Also note that, based on total pressures, the ‘Boys’ defense should have totaled five fewer sack this year than they did, i.e. they got lucky with a sack total that overestimates how well they really rushed the passer.
Ryan certainly got extremely unlucky with injuries this year, but that is already accounted for in the bulk stats. The fact that the efficiency stats are worse than the bulk stats suggests the Cowboys played worse than traditional numbers indicate, regardless of how many injuries they had.
That’s not to say that Ryan should have gotten canned, however. I personally thought he deserved one more year, but that doesn’t mean the Cowboys made a poor decision. We should all try to withhold judgment until we see who the team brings in. Remember, it doesn’t really matter if someone “should” retain their job, but really whether or not they’re the best person for it. If the Cowboys bring in a superior option to run the defense, then they obviously made the right move.
Jonathan Bales is the founder of The DC Times. He writes for DallasCowboys.com and the New York Times. He's also the author of Fantasy Football for Smart People: How to Dominate Your Draft.