The analysis used the best advanced stats available to judge quarterback play and properly weighed the confidence we should have in a quarterback’s performance based on their sample size.
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I will apply 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 for 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 PFF analytical quarterback rankings through Week 2, I’ve provided some visualizations to give proper context to how these quarterbacks performed in PFF grade and EPA per play and some important data splits that show the potential for regression moving forward.
Jimmy Garoppolo has performed well enough from an efficiency standpoint to hold off Trey Lance for at least another week. However, his grading hasn’t been very strong. Patrick Mahomes has had a similar 2021, with the league’s best EPA per play but only a middling PFF grade.
Tom Brady is on the other side of the spectrum, with an outstanding PFF grade and a handful of big negative plays holding down his efficiency.