Could Aaron Donald be the best defensive tackle ever?
Though Pro Football Focus wasn't around in the days of "Mean" Joe Greene or Merlin Olsen, we have been grading games since 2006, and have 13 seasons worth of play-by-play grading in our database. All of that data indicates that it would be difficult for any pass-rusher to scale higher peaks than the ones Donald is ascending right now.
We can't definitively put Donald in the context of the older all-time greats, but we can quantify how much better Donald is than any defensive tackle we have seen over the last decade-plus of action. In doing that, we can put into focus the enormity of what he's doing and the difficulty of anyone surpassing him.
Donald isn't just the league's best interior pass-rusher ...
When focusing only on interior pass-rushers, the gap between him and the field is quite wide. Donald leads Geno Atkins and Fletcher Cox, the second- and third-most productive interior pass-rushers since 2014, by 79 and 83 pressures, respectively. To provide context, those figures would lead the league more often than not in a single season.
Donald has out-graded every interior defensive lineman by a comfortable margin in every season since 2015. That includes league-high overall grades of 93.0 in 2015, 92.6 in 2016, 94.4 in 2017 and a career-high 95.0 a season ago. He has also posted the best pass-rushing grade among all interior D-linemen in those seasons, as well.
But that's not where his dominance ends.
... he is leaps and bounds above all pass-rushers
Donald is the entire league's best pass-rushing force, dominating an era in which pass-rushing is as important as ever.
Outproducing the best interior rushers since entering the NFL in 2014 is one thing; outperforming edge rushers is another. Since joining the league, Donald has 20 more total pressures (combined sacks, hits and hurries) than any other pass-rusher. He has done that on fewer pass rushes than any of the other top defenders, which also gives him the highest win rate in the league, despite being an interior pass-rusher.
Edge rushers usually generate significantly more pressure than interior players thanks to having more space to operate, plus the difficulty for the offense to execute double-teams in that space, but Donald generates more pressure than any edge rusher. The second- and third-most pressures over that period belong to Von Miller and Khalil Mack, arguably the two best edge rushers over the past several seasons, but neither can touch Donald.
Donald's PFF grade -- which factors in speed and decisiveness of pressure as well how often it happens -- puts him even farther ahead of the pack. His career grade rushing the passer is 95.4, 3.0 points ahead of Miller and even farther ahead of Mack.
He hasn't reached his ceiling yet
Perhaps the most amazing thing about Donald is that he's still getting better. The 2018 season marked the best PFF grade of his career, as well as the highest pressure total he has amassed, and he has 50 more total pressures than any other player over the past two seasons. Over those last two years, Donald leads the NFL by more total pressures than Ndamukong Suh was able to tally alongside him in 2018. Again, Donald's pass-rush win rate was on another level. Only four other players had a win percentage higher than 20% over the season, but Donald was the only player in the NFL above 25% (25.9%).
When you start talking about all-time greats, the concept of affecting the game in ways besides raw production quickly surfaces. Sure, Donald has more sacks than Cortez Kennedy, but Kennedy was always double-teamed, that's why his production is lower. Or so the argument typically goes.
Well, PFF can quantify that, and Donald was double-teamed on 61.4% of his pass rushes in 2018. That's a huge figure, yet Donald still won more often than any other pass-rusher.
His value shows no signs of slowing down
His level of dominance unmatched, Donald has actually improved his grade in each of the past two seasons with are no signs of slowing down anytime soon. No defensive player at any position has put forth the start to a career that Donald has in the PFF era and as scary as it may sound for the rest of the NFL, at just 28 years of age, Donald's best football is likely still ahead of him.
PFF is beginning to quantify the value of players that goes beyond the production they generate. Using PFF's WAR (wins above replacement) metric over the past three seasons, Donald has generated roughly two full wins in the regular season for the Rams, tops among defensive linemen.
While he had a statistical breakout in 2018 on paper, recording 20.5 sacks -- 8.5 more than his previous career high -- it was a continuation of the steady improvement he's shown throughout his career. Pressure is generally a lurking variable when it comes to projecting outlier seasons for pass-rushers, and Donald has been a terror in that department since the Rams drafted him. He generated 113 total pressures in 2018 in 703 pass-rushing snaps, where in 2017 he had 102 in 558 snaps, both off-the-charts numbers for defensive players not named J.J. Watt.
Ultimately, until PFF goes back and grades the older all-time greats, we won't be able to directly compare them to Donald. But based on more than a decade of watching and analyzing every player on every snap, it is getting harder to imagine that anybody has ever topped the level that Donald is currently at. All that remains for Donald to cement his legacy is maintaining longevity at the top.