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RTN: A Different View of the Cowboys’ Defense

Posted Jul 16, 2013


Training camp is right around the corner. Your Dallas Cowboys are just a few weeks away from live game action. It’s time to look ahead to the 2013 season.

To do that, though, we need to understand what went right and wrong in 2012. And while lots of stuff went wrong, it would be a mistake to conclude that, since the results weren’t up to par, the entire process needs to be changed. Quality decision-making leads to poor results all of the time, and vice versa; hitting on 19 in blackjack will lead to a positive result from time to time, but it’s always the wrong decision.

In order for us to comprehend what truly needs to be changed, we have to understand randomness; if the Cowboys did everything right in a particular facet of the game but just got unlucky, they don’t need to change anything. Head coach Jason Garrett is correct when he says the team shouldn’t change just for the sake of change. They should change because it makes them a better football team.

Last week, I attempted to filter out some of the luck involved with point totals by comparing total offensive points to expected points:

When you hear Joe Buck cite the offensive ranks for each team playing on FOX on Sunday afternoon, you’re typically hearing where they stand in terms of either total points or total yards. I’ve explained in the past that those are really poor measures of offensive talent because they do little to isolate an offense from their defense and they don’t account for things like tempo or game situations.

I’ve also explained why a better metric, perhaps the best out there, is “Expected Points Added.” EPA is a measure of how many points an offense “should have” scored based on how they played. It factors in historic success rates and game situations to determine the most likely outcome in any particular situation. A first-and-10 at your own 20-yard line has historically been worth a net of 0.34 points, for example. Because of that, an offense holding possession in such a situation at the start of the third quarter would be a slight favorite to win the game, at about 52 percent, given that the score is tied and their EPA is positive.

In any event, EPA is awesome in that it does a really solid job of capturing performance independent of luck; it’s primarily a measure of how many points a team should score given how they perform in specific game situations. Like Garrett, EPA intelligently emphasizes the process over the results.

So we have a metric that is filled with noise (total points) and one that’s not (EPA). If we compare the two, we should get a decent idea of which teams got the luckiest – that is, which overachieved and which underperformed relative to how well they actually played.

Well, we can use EPA to grade defenses as well. By looking at game situations, we can calculate how many points a defense “should have” given up based on their performance. Just as with the offenses, we can compare EPA to actual points allowed to determine which teams were luckiest and unluckiest in 2012.

Points Allowed Versus EPA

Below, I charted each team’s 2012 rank in both points allowed and defensive EPA. The teams are sorted based on the difference between the two numbers.

 

The teams closest to the top are those that ranked a lot higher in EPA than in actual points allowed. Notice the sort of teams listed there – the Cardinals, Jets and Titans – all of whom had poor offenses. These numbers suggest that the defenses for those teams were far better than the points indicated; if they get moderately better offensive play, the defenses will be placed in better situations and should improve significantly in terms of total points allowed.

At the bottom, you see that the Falcons, Colts, and Giants’ defenses were the luckiest. All got quality offensive play, and all were lucky to allow as few points as they did. It’s also interesting to note that the Seahawks, the team with the defense that some believe the Cowboys will imitate in 2013, generated the seventh-best defensive EPA mark despite allowing the fewest points in the NFL.

And right in the middle, again, are the Cowboys. Based solely on how the players on the field played, the ’Boys overachieved just a bit. Of course, these numbers don’t take into account the massive number of injuries the Cowboys experienced on defense last year. If there’s one change that will help the Dallas defense the most, it’s not a switch in opening day starters or defensive coordinator, but simply better health.

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