The analysis used the best advanced stats available to judge quarterback play and properly weighed the confidence we should have in a signal-caller's performance based on their sample size.
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I applied the same framework to quarterbacks throughout the 2021 season, keeping an eye on how each quarterback’s current-year performance aligns with our best estimate for his skill level based on his entire career.
Even in a single season, there can be drastic differences in sample sizes for quarterbacks. This means that comparing unadjusted rate stats side by side can give too much credit to those who aren’t a big part of their offense and too little credit to those who dominate as their team's No. 1.
I utilize a statistical technique called Bayesian Updating to solve the sample size issues. It is a method PFF has used many times in the past, notably when we looked at a number of different draft classes, why the New York Jets needed to draft a quarterback in 2021 and whether Carson Wentz had much to offer a new team in 2021.
You can find details of how Bayesian Updating is implemented here, including a primer on how we build a posterior belief (or projection) based on historical quarterback results and then update the beliefs (projections) for each quarterback with their actual NFL results on a play-by-play basis.
CONTEXTUALIZE 2021 PERFORMANCE
Before I dive straight into the final PFF analytical quarterback rankings after the 2021 NFL regular season, I’ve provided some visualizations to give proper context to how these quarterbacks performed in PFF grade, EPA per play and some important data splits that show the potential for regression moving forward.
One of the biggest drivers of overall EPA efficiency is quarterback performance on third and fourth down. The reason these plays have such a large impact is that the upside for conversions is tremendous. Third-and-medium or third-and-long plays determine whether a team needs to punt and essentially turn the ball over or settle for a field goal rather than pushing forward for a touchdown.
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Because late downs are so high-leverage, the range of efficiency for quarterbacks on those plays is much higher and has a more substantial impact than earlier downs. Jimmy Garoppolo and Kyler Murray have been able to perform well in those high-leverage situations.
Another piece of context for these small-sample results is play under pressure. Over a season, a quarterback needs to play well from a clean pocket and under pressure to lead the NFL in overall efficiency.
Clean-pocket passing is more stable, so the hope would be quarterbacks with strong clean-pocket play — such as Aaron Rodgers — will play better under pressure the rest of the season. There are definitely certain quarterbacks who can consistently play better under pressure than others, but it can be tough to identify them in a small sample.
THE 2021 ANALYTICAL QUARTERBACK RANKINGS
The table below ranks the quarterbacks according to a combination of the Bayesian estimates for PFF grade and EPA per play based on what we've seen over the course of the 2021 NFL regular season.
I’ve included the number of plays in the first data column for context, plus the separate grade and EPA ranks, the total ranking, and the previous week’s ranking.
The last column has each quarterback’s career Bayesian ranking, updated from my offseason article based on what has happened this year.
The ageless wonder Tom Brady sneaks ahead of Aaron Rodgers to end the season as the top quarterback for 2021. Brady benefited from a strong Week 18 performance, and the model has more confidence in his outperformance with a sample of plays that is 175 greater than that for Rodgers.
Joe Burrow and Justin Herbert flip spots in the last week, but both fan bases can be confident they’ve found their franchise quarterbacks. The big riser of the week was Dak Prescott moving up to No. 8 and Patrick Mahomes barely making it into the top 10.