As we get closer to the start of the regular season, the debates begin to multiply. Is Jay Cutler really the right person to lead the Bears? Which rookie QB will have the best season? Who would win in a fight between J.J. Watt and Gronk? What the hell is going to happen with Tom Brady?! But there is one debate that seems to have been going on for decades, and I’m not talking about the Deflategate hearing. I’m talking real defense. Because in the NFL, there are two main base defenses: the 4-3 and 3-4.
The 4-3 is the older defense of the two and is more thought of as the standard. It consists of four defensive linemen and three linebackers. In the 3-4 there are three defensive linemen and four linebackers.
Now, besides just the differences in number of players at the positions, the two base defenses differ in their purposes, strengths and weaknesses. Although I consider myself fairly knowledgeable about the two, I am by no means an expert, nor do I claim to be. However, in a nutshell, the two base defense differ in the way that they attempt to apply pressure.
In a 4-3 defense, pressure is mainly created from the front four. One tackle occupies two blockers, and the rest of the line get one-on-one match-ups. Linebackers do their fair share of blitzing, but their main responsibility is stopping the run and guarding against the pass.
In a 3-4 defense, the pressure is mainly created from the backers. The job of the defensive line is to occupy gaps, and occupy multiple offensive linemen. The outside linebackers in a 3-4 have a much greater pass rushing responsibility, and the fact that there are two middle linebackers allows for a lot of creative blitzes and coverages.
Now that Football 101 is over, it’s time to address a question that has always existed: which base defense is best? For a long time most NFL minds thought that the 4-3 was the way to go. Only in the last few years (mid 2000s) did the 3-4 start to become as popular as it is.
A lot of credit for popularizing the 3-4 is most likely due to the success the Pittsburgh Steelers have had over the years they have utilized it. As of this year, there are 17 NFL teams that operate out of a 3-4 base defense, and only 15 that operate out of a 4-3.
When comparing the Pro Football Focus defensive rankings for teams that ran the 4-3 v. the 3-4, a few interesting things pop up. Looking at the overall rankings, the difference between the median 3-4 team and 4-3 was .5, for run defense it was 3.5, for pass defense 1.3 and pass coverage -4.4.
Let’s ignore pass coverage for now, because that is more dependent on the defensive backs than the set-up of the front seven. It seems to be that 3-4 teams do better when it comes to defensive line performance. But “better” is really a .5 or a 3.5 difference.
To do this, I used a technique called bootstrapping. Basically what it does is for a given data set, it randomly assigns the labels of 3-4 and 4-3 to the Pro Football Focus rankings to see what percentage of the time were the results as extreme as the actual. For overall it occurred about 40% of the time, for run defense it was 18% and for pass rush it was 29%.
None of the numbers are really low enough to conclude anything for sure. They tend to suggest that 3-4 base do a better job of stopping the run and rushing the passer, but it could have just been a bit of a lucky year.
One reason why the link between base defense and performance is not very strong is that teams just don’t use it that much. In 2008, NFL teams were in a 3-4 or 4-3 for 54% of snaps, by 2011 it was done to 47%, and by last year it was down to 43%. The link will not be very strong when you spend more than half of your snaps outside of your base defense.
We may never get an exact answer to the question, because there may not be one. Teams can succeed in either base defense. It most likely comes to coaches and the players themselves. Still, you can bet that if a definitive answer ever does rise, that half of the NFL’s teams will be making the switch, ASAP.