Brock Purdy is 12-3 as an NFL starter in the regular season. His passer rating over that year-plus stint is a league-leading 112.2. He is operating within the confines of Kyle Shanahan’s low risk, high reward offense and thriving.
Does that make him 2023’s best quarterback? The numbers say yes, even if watching his game tape fails to inspire the same confidence.
Purdy has been an upgrade over Jimmy Garoppolo in an offense meant to blunt the liabilities of a shaky downfield passers with motion, movement and a ton of open space to create massive gains after the catch. But when pressed to fit big throws into tight windows downfield, the second-year passer has struggled. His 24 deep throws rank 23rd most in the NFL, a number that looks better than it is given the rash of quarterback injuries that have shaken up starting lineups this fall.
All five of his interceptions this season came in a three-game losing streak that stands as the only blemishes on his team’s 2023 record. Four came on throws at least 13 yards beyond the lin of scrimmage, showcasing his struggles when asked to force the ball downfield in disadvantageous situations. Purdy is very good, but he’s not in the circle of trust just yet.
That doesn’t keep him from holding down the top spot in this week’s advanced stats QB rankings — by a wide margin, in fact.
Let’s talk about those stats. Expected points added (EPA) is a concept that’s been around since 1970. It’s effectively a comparison between what an average quarterback could be expected to do on a certain down and what he actually did — and how it increased his team’s chances of scoring. The model we use comes from The Athletic’s Ben Baldwin and his RBSDM.com website, which is both wildly useful AND includes adjusted EPA, which accounts for defensive strength. It considers the impact of penalties and does not negatively impact passers for fumbles after a completion.
The other piece of the puzzle is completion percentage over expected (CPOE), which is pretty much what it sounds like. It’s a comparison of all the completions a quarterback would be expected to make versus the ones he actually did. Like EPA, it can veer into the negatives and higher is better. So if you chart all 32 primary quarterbacks — the ones who played at least 176 snaps in 11 weeks — you get a chart that looks like this:
Top right hand corner is good. Bottom left corner is bad. Try splitting those passers visually into tiers and you get an imperfect eight-layer system that looks like this:
These rankings are sorted by a composite of adjusted EPA and CPOE to better understand who has brought the most — and the least — value to their teams across the small sample size. It’s not a full exploration of a player’s value, but it’s a viable starting point. Let’s take a closer look.