Who Wins Games for the Cowboys: Offense or Defense?

Some of the more lively debates among Dallas Cowboys fans take place when the talk turns to the roles the offensive or defensive units play in winning or losing games.

The arguments exchanged in those debates typically sound something like this:

• In 2011, the offense scored less than 17 points in five games. The Cowboys lost all five games. Therefore the offense sucks.
• In 2011, the Cowboys were 6-1 in games in which the defense held opponents to less than 20 points. Had the defense held more opponents below 20 points, the Cowboys would have made the playoffs. Therefore the defense sucks.

If, like me, you're still living in a world where every offseason you think that the current year's team will be a reincarnation of the 13-3 2007 team, you may be surprised to find that over the last four seasons, the Cowboys have compiled a paltry 34-30 record. So who's at fault here?

One way to understand the contributions of each unit is to look at 'wins over average' for each unit, and that's what we'll do after we make like David Lee Roth and jump.

'Wins over average' is a metric developed by Doug Drinen at Pro-football-reference.com (PFR) in a post on adjusting QB records, back in the days before PFR closed down their blog. I've taken his approach and modified it slightly to look at total offense and total defense.

Think back to the 18-16 win against the Redskins last year. Did the offense or the defense win that game for the Cowboys? Arguably, if anybody won that game it was the kicker, who connected on six field goals. But for our purposes, the defense probably won that game by holding the Redskins to 16 points. The offense certainly didn't win it, they didn't score a single TD. You could go through almost every game and find arguments like this or like the arguments outlined in the lead-in above. But instead of subjectively evaluating each game, I'll approach this with a more objective, stat-based approach. This is how it works:

Wins over Average: As our measure of difficulty for the offense, we'll use points allowed, because it's a lot harder for an offense to win a game if their defense gives up 30 plus points than if they give up 10. For the defense, we'll look at points scored by their offense, as it's a lot harder to hold opposing offenses in check when your own offense is only scoring 10 points rather than 30 points.

In the table below I've crunched the regular season number for all NFL teams for the last six years, so that's 3,072 scores. I've formed five clusters by points allowed/points scored and looked at the winning percentages for each.

Obviously, one team's points scored is the other team's points allowed, so the table below contains the same numbers for offense and defense, just reversed:

How to read the table: An NFL offense almost always (491 vs 30) scores more points than the other team if the defense allows ten points or less. The NFL average winning percentage is .942 in those games. At the other end of the spectrum, when your offense scores 32 points or more, your defense is almost always (468-38) able to hold the opposing team to fewer points for a winning percentage of .925

Cowboys offense and wins over average: The Cowboys have a record of 12-0 over the last four years when the defense allowed ten points or less. The average NFL team would be expected to win 11.3 games (12 games x .942), so the Cowboys have 0.7 wins over average in this bracket. In the 11-17 bracket, the Cowboys have a 9-3 record, where an average NFL team would be expected to win 8.6 games (12 games x .721). The Cowboys offense therefore gets the credit for 0.4 wins over average. Across all brackets, the wins over average total +2.9 games.

Cowboys defense: The Cowboys have a record of 1-7 over the last four years when the offense scored ten points or less. The average NFL team would be expected to win 0.5 games (8 games x .058), so the Cowboys scored 0.5 wins over average in this bracket. Across all brackets, the wins over average total -1.6 games the defense as per the table on the right.

So statistically, the Cowboys offense generated slightly more wins over average than the defense, but not by a wide margin. Both units struggled a lot over the last couple of years, and the difference between the two units isn't large enough to be able to point at one specific unit as the reason for the Cowboys' 34-30 record over the last four years.

It therefore stands to reason that it will take an improved performance on both the offense and the defense to make sure the Cowboys win enough games this season to make the playoffs again.

Coming up next, another look at Wins Over Average - but this time it'll about quarterbacks.