If your team just signed a solid yet one dimensional run stuffing interior defensive lineman, you should not be excited. Teams have been throwing lots of cash at these types of players. Players like DJ Reader, Michael Pierce, Michael Brockers, Jordan Phillips, and Linval Joseph all just signed massive deals with AAVs from $8.5-13.25 million. Flat out, none of these signings provide positive value for the following reasons, first run defense is the least important part of a defense and second it is not hard to find a IDL who can stop the run.
Run Defense is Not That Important
In order to measure how important each component of a defense is, I used various PFF grades and measured their relationship with a teams’ wins that season. I compiled data from the past 4 seasons and the results very clearly indicated run defense is not essential to win in the NFL.
As the graph above depicts, there is practically no relationship between a team’s PFF grade for run defense, and their amount of wins. For reference, the r-squared between pass rush and wins, and coverage and wins were 0.121 and 0.274 respectively.
If we take a step back from the data and think, this does make sense. The NFL is a passing league and there is no denying it. The most important facets of the game are pass offense and pass defense. Also, a team that has a lead for the majority of the game does not need a great run defense because teams will be throwing the ball much more to try to catch up quickly, rather than burn the clock running the ball.
But, there is more evidence that spending big on IDL is not an efficient use of cap space, below is the relationship between the % of cap space spent on IDL and wins from 2019.
The r-squared of the graph above is only 0.02 so there is practically no correlation between spending on DL and the amount of wins a team has, further proving that spending big for DL free agents is an inefficient use of cap space.
Run Stuffing IDL Are Not Hard to Find
In addition to run defense not being very valuable, finding an IDL who can stop the run is not difficult. In 2019 there were 154 IDL that played more than 100 snaps, and among those players 54.5% had a run defense grade of 65 or above (considered slightly above average or better), and 18% had a run defense grade of 75 or above (considered good or better). Contrast this with IDL pass rushing grades, 28.5% had a grade of 65 or above, and 9% had a grade of 75 or above. The ability to rush the passer is much more valuable than the ability to stop the run, and run stopping IDL are not scarce, so it does not make much sense to pay top dollar for a good run stuffer.
So, fans do not get excited about your team spending big to stop the run when many values can be found who will give adequate production, and when that cap space would be used more efficiently if spent on something much more important like offense, coverage, or pass rush.
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