As a football fan, you've probably heard mantras like "defense wins championships" or "offense sells tickets, defense wins games" literally hundreds of times. Heck, you may even believe those mantras. But just because something is repeated again and again doesn't mean it's necessarily true. Especially not lately. Here's a look at the four worst pass defenses last year as measured by passing yards allowed. Notice that the table contains the two Super Bowl participants and two other teams that made it to the divisional playoff round.
|NFL Rank||Team||Passing yards allowed||Record|
The Patriots and Packers defenses were not just bad, they were historically inept. The previous NFL record for passing yards allowed in a 16-game regular season was held by the 1995, with 4,541 yards. The 2011 Patriots and Packers had the worst pass defenses in league history, yet combined for a 28-4 regular season record. Were these teams' defenses really that bad or are these numbers perhaps a little misleading? After the break, we look this in a little more detail and also try to figure out what this means for the .
Last season illustrated clearer than perhaps ever before how dominant the passing game has become in the NFL, and by extension, how passing defenses have struggled:
- There were 121 individual 300-yard passing performances in 2011, handily beating the previous record of 104 from 2009.
- There were 18 individual 400-yard games in 2011, beating the single season record of 14 set in 2004 and 1986.
- Four quarterbacks passed for more than 4,900 yards: Drew Brees (5,476), (5,235), Matthew Stafford (5,038) and Eli (4,933). In the entire history of the NFL, there were just two quarterbacks who surpassed that mark (Dan Marino, 5,084 in 1984 and Drew Brees, 5,069 in 2008).
And while the NFL and the people who are paid to report about the NFL have conditioned us fans to look at volume stats like the ones above, the number of yards you accumulate or give up has almost no correlation with whether you win or lose a game in the NFL. How much someone passes or runs for can make for nice anecdotal discussions in the context of fantasy football, but has next to nothing to do with winning in the NFL.
Today, winning in the NFL is all about passing efficiency. The best offenses are those that pass the ball the most effectively, the best defenses are those that prevent their opponents from passing it effectively. The best teams in the league are those that do both most effectively.
One way to look at that is by calculating the difference between a team's passer rating on offense minus the defensive passer rating. This passer rating differential effectively tells you how much more effective a team is at passing the ball relative to its opponents and, and it can be a very strong indicator of team strength.
Here are the top ten teams from 2011 as ranked by passer rating differential:
|Passer Rating Differential, 2011
|Rank||Team||PR Offense||PR Defense||PR Differential||Rank||Team||PR Offense||PR Defense||PR Differential|
|1||Green Bay||122.6||80.6||42||17||San Diego||88.7||92.5||-3.8|
|4||New England||105.7||86.1||19.6||20||Kansas City||73||79.1||-6.1|
|10||New York Jets||78.4||69.6||8.8||26||Washington||73.3||87.4||-14.1|
|12||New York Giants||92.9||86.1||6.8||28||Denver||73.5||93.1||-19.6|
|Playoff teams highlighted in bold|
You think this is all some fancy-pants stat mumbo-jumbo without any real bearing on actual game results? Here's a simple graph that plots the Passer Rating Differential of all 32 NFL teams against their wins in 2011:
The graph illustrates a fairly simple truth: the higher your passer rating differential, the higher the number of wins a team had last year. Conversely, the teams with the lowest number of wins had some of the worst passer rating differentials (PRD).
In statistics this relationship between wins and PRD is called a correlation. The strength of the correlation is measured by the "correlation coefficient". The correlation coefficient measures the relationship between two variables. This coefficient is often referred to as "r²" and is expressed as a number between 1 and -1. The closer the r² number is to 1 or -1, the stronger the relationship between the two variables. The closer it is to zero, the weaker the relationship.
R² between PRD and wins in 2011 was 0.80, an astonishingly high correlation. It is almost as good as scoring differential (0.85) at predicting the W/L record of an NFL team.
Now for a little detour, just for fun. Here are some correlations with 2011 W/L records and a collection of other stats:
|Passer Rating Differential||0.80|
|Passer Rating Offense||0.62|
|Passing Yards OFF||0.34|
|Passer Rating Defense||0.31|
|Passing Yards DEF||0.08|
*ANY/A: Adjusted net passing yards per attempt = (Passing Yards + (Passing TDs)*20 - (INTs thrown)*45 - Sack Yards) / (Passing Attempts + Sacks)
*Y/A: Yards gained per pass attempt (Passing Yards / Passes Attempted).
*NY/A: Net yards gained per pass attempt, which is basically Y/A adjusted for sacks (Passing Yards - Sack Yards) / (Passes Attempted + Sacks).
Passer rating differential beats almost any other available stat in terms of how closely it correlates to wins in the NFL. It follows that as a team, you should do everything you can to improve your passer rating differential, no?
Back to the original question: were the Packers and Patriots defenses really that bad or are the stats misleading? The answer is: Both. Those defenses were atrocious against the pass. But being bad against the pass is, taken by itself, almost a non-issue. The correlation between passing yards allowed and W/L record in 2011 is 0.08 - virtually non-existent.
But a bad pass defense only remains a non-issue for a team as long as its offense keeps producing. The problem obviously is, once you manage to stop the Packers or Patriots offense, their defense will not be able to compensate.
All of which brings us to the Dallas Cowboys. The Cowboys are ranked ninth overall in passer rating differential. They achieved this on the strength of the number four passing offense (100.1 offensive passer rating) paired up with the 25th ranked passing defense (88.4 defensive passer rating).
Last season, the Cowboys combined one of the most efficient passing attacks in the league (and the most efficient in franchise history as measured by passer rating) with a very poor pass defense.
We've established that passer rating differential is one of the stats most closely linked to winning in the NFL. It follows that the quickest way to get more wins for the Cowboys in 2012 is to improve the passer rating differential. The Cowboys already have an elite passing offense, so there isn't really that much room for improving the passer rating differential via the offense. That leaves the defense.
The Cowboys' best chance for improving their W/L ratio in 2012 is to improve their pass defense. In fact, I would strongly advocate that the Cowboys spend at least their top three 2012 draft picks on defense, and I would not object at all if they spent all of their draft picks on defense. And really, the only question left is more of a philosophical question: Is the quickest route to an improved passing defense an improved pass rush or an improved secondary?