# Difference Between 3-4 And 4-3 Defenses (Part 2)

In a previous post, I detailed how the 3-4 defenses over the past 10 seasons have, on average, outperformed 4-3 defenses. However, it’s possible that those 3-4 defenses simply had better players and that the 3-4 only appears to be the better scheme.

This time around, to account for each individual defense’s strength, I used a multivariate regression. The dependent variable in each model was a measure of success—EPA, WPA, and Success Rate (SR). The variable of interest was whether or not the defense was a 3-4 (a 1 if it was and a 0 if it wasn’t). The resulting coefficient of this variable represents the advantage of the 3-4 over the 4-3.

Each individual team was also assigned a dummy variable intended to capture the team-specific strength of their defense. Conveniently, this technique also accounts for the general year-by-year improvement in the effectiveness of NFL offenses.

There were 318 cases (team-years), from the 2000 Arizona Cardinals...to the 2009 Washington Redskins.

The results of the regressions indicated that the advantage of the 3-4 was not due to a coincidence of exceptionally talented players who happen to play in 3-4 schemes. In fact, the advantage of the 3-4 is even larger when individual team strength is accounted for.

This time, in addition to comparing WPA and EPA, I compared the 3-4 and 4-3 in terms of Success Rate (SR). SR is defined as the proportion of plays that result in positive EPA. Although it is a simple derivative of EPA, it is important in how the teams themselves perceive the game, a concept I'll explain in a later post.

Here are the key results of the regressions. Like before, negative numbers are better. Spikes, kneel downs, and aborted plays are excluded. The resulting coefficients for the 3-4 defenses were significant at the 0.05 level, except those noted by an asterisk, which were significant at the 0.10 level.)

Per Play
Per Game

SR Overall
-1.4%
-

SR vs. Pass
-1.5%
-

SR vs. Run
-1.4%
-

EPA Overall
-0.038
-2.48

EPA vs. Pass*
-0.041
-1.50

EPA vs. Run
-0.036
-0.98

WPA Overall
-0.00103
-0.066

WPA vs. Pass*
-0.00109
-0.040

WPA vs. Run
-0.00095
-0.026

According to the regression results, defenses employing the 3-4 tend to yield 1.4% fewer successful plays than 4-3 defenses. They tend to allow 2.5 fewer EPA per game, giving their teams an additional 6.6% greater chance of winning each game. This would roughly be the equivalent of home field advantage.

Contrary to the results seen in part 1, the regression results suggest the strength of the 3-4 is against the pass, although not by much.

Teams all around the league are switching to the 3-4 for a reason, and the stats appear to back up the belief that it's a better scheme against the modern NFL offense.

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