You know an issue has broken out of the football world and into the mainstream when those who don’t participate in the discourse on a daily basis start discussing a particular topic.
Like Brock Purdy.
The Brock Purdy discourse has dominated the past calendar year and will reach a fever pitch this weekend when he makes his first Super Bowl start in Super Bowl LVIII against the Kansas City Chiefs. As the former “Mr. Irrelevant” evolved into his role as starting quarterback for the San Francisco 49ers, the discussion turned from a “heartwarming underdog story” to “is he actually a good quarterback, or is he simply backed by a creative offensive system while surrounded by a team from Monstars? ?”
So imagine my surprise when Williams driver Logan Sargeant said this to me and other media members about Purdy during a roundtable discussion in New York City on Monday: “You can’t bet against Patrick Mahomes, but I’d like to see Brock just win. because the underdog story earns him a lot of hate that he doesn’t deserve.
As with many football-related debates, two things seem to be true: first, the two camps appear to be developing as they always do, with the ‘film watchers’ on one side and the ‘analytics’ on the other. Second, the answer to the above questions probably lies somewhere in the middle, an idea we’ll get to in a moment.
But for now let’s focus on the analytical arguments in Purdy’s favor, of which there are many. As someone who spends most of his football analysis watching film, I first believe that looking at all available pieces of data is critical when constructing an argument and reaching a conclusion. The more information you have, the better substantiated your opinion.
Let’s start with Expected Points Added, or EPA, a basis for many analytical arguments. As defined by Pro football focus EPA “…is a measure of success that defines the value of each play by the effect it has on the offense’s probability of scoring. For each game, EPA is awarded equally to both teams, and the metric is quite reliable in identifying the best teams in football. It is common to discuss EPA per play (EPA/Play) so that the statistic is normalized for any differences in the total number of plays played.
Specifically, EPA is the difference in the “expected points” before and after a game. So if a play is successful the team gets EPA, but if the play fails the team loses EPA. The statistic “is an estimate of how many points a team will score during a stage, given the current situation (Down, Distance, Remaining Time, etc.). Intuitively, the closer a team gets to the opponent’s end zone, the higher the expected points of the drive are.”
With that in mind, let’s look at this chart RBSDMwhich maps EPA/Play and Completion Percentage over Expected (CPOE), which we will look at next:
As you can see, Purdy led all quarterbacks with an EPA/Play of 0.338 this season. Dak Prescott ranked second, with an EPA/Play of 0.245.
If you expand the time frame a bit and look at 2022 and 2023 together, Purdy still comes out on top in this metric:
Purdy’s EPA/Play over these two seasons is 0.298. Patrick Mahomes, his opponent on Sunday, is second with an EPA/Play of 0.221 for 2022 and 2023 combined.
Now let’s look at the second metric in this chart, which is CPOE. Ben Baldwin, the mind behind it RBSDM, has created a model that outlines the chances of a pass being completed given several factors, including downhill, distance, meters to go, air meters and more. This allows you to calculate the ‘expected completion rate’. Then you compare that to the actual completion percentage for a quarterback, and you can find their CPOE.
For example, a five-yard screen pass to a running back behind the line of scrimmage has a higher expectation of completion than a 30-yard post in double coverage.
If your expected completion rate for this metric is 70% and your actual completion rate is 75%, you have a CPOE of 5%. This number can be negative: for example, in 2023, Gardner Minshew had a completion rate of 65.6% and an expected completion rate of 68.9%, for a CPOE of -3.3.
Now let’s return to Purdy and the 2023 chart:
Purdy posted a CPOE of 5.4, which led all quarterbacks in 2023. Josh Allen came in second with a CPOE of 5.0. When you expand the time frame to 2022 and 2023, Purdy clocks in at third in this metric with a CPOE of 3.6, behind Geno Smith (4.2) and Jacoby Brissett (3.7).
There is another stat that could work in Purdy’s favor, namely Adjusted Net Yards per Attempt (ANY/A). This “includes passing yardage, sacks, touchdowns and interceptions. ANY/A is simple to calculate, easy to understand and has a strong correlation with the points scored,” noted by Inside the pylon.
Purdy posted an ANY/A of 9.01 this year, leading all passers. Tua Tagovailoa checked in second with an ANY/A of 7.48.
Purdy is the first quarterback to finish the season with an ANY/A above 9.00 since Matt Ryan won MVP in 2016.
The counterargument to these points is often, “These are just a few stats” and “Purdy’s supporting cast, as well as Kyle Shanahan’s offense, make it easier for him.” As for CPOE, there’s a counterargument that Purdy’s success in that area is due more to receivers saving him than his own play on the field.
Still, CPOE also illustrates that Purdy is willing to challenge some tighter throwing windows and/or push the ball deeper down the field than you might expect. On that second count, Purdy posted an Intended Air Yards (IAY) of 8.3 this season Next generation statisticswhich placed him 14th in the competition.
Mahomes had an IAY of 6.6 this year, which ranked him 40th.
As for the supporting cast argument, an interesting statistic debuted this week thanks to EJ Snyder and Arjun Menon called Quarterback Deficiency Differential or QBDD. Here, Snyder explains the metric they created:
So… I invented a new statistic. We always talk about how important support is for a QB, but I couldn’t find a stat that showed what I wanted, so I created one. And then… I had to make another one. So yes, I made 2 statistics. Here’s a video (and a thread) about why, how, and who helped: pic.twitter.com/FfAEGs9DeU
— EJ Snyder (@VoetbalEJ) February 6, 2024
They wanted to try to quantify how much help a quarterback received from the players around him. The result was QBDD, which they mapped here:
This comet tail chart shows QBS (marked by the QB photos) and their EPA/play mark (the sharp point). Long tail pointed right = outperformed their support. Short tail either way = performed pretty similar to support. Long tail pointing left = underperforming relative to their support pic.twitter.com/PscYoLOpTA
— EJ Snyder (@VoetbalEJ) February 6, 2024
Here’s a zoomed-in look at Purdy, top right:
In their findings, Purdy was supported by his surrounding talent, but still performed fairly equally [his] support.”
Again, another data point, but an interesting one.
As always, there will be detractors. Many can – and will – point to Purdy’s performance in the playoff games this season and argue that the 49ers may have overcome some subpar play. As mapped for example by PFF, Purdy has three Turnover Worthy Passes (TWP) this playoff season and a TWP% of 3.8%.
According to him, Mahomes has yet to throw a turnover-worthy pass PFFs mapping.
So those who doubt Purdy will have their own numbers to point to.
But as noted above, I’m probably someone who’s more in the “movie watcher” camp, so there are some arguments to be made in Purdy’s favor there too. Arguments and examples where Purdy may be doing more in the 49ers offense than his predecessors, creating opportunities for San Francisco outside the structure of the offense. This is something I highlighted earlier this season when San Francisco and Purdy split the Pittsburgh Steelers.
Games like this stand out, with Purdy quickly reacting to TJ Watt falling into the throwing lane and coming up with a “Plan B:”:
Not only does Purdy make the initial no-throw decision by pulling the ball down and avoiding an interception thrown straight to Watt, but he turns his gaze back to his left and picks out Christian McCaffrey on a quick, slant route on. The play only yields a seven-yard gain, but in a snap where the defense had everything in place to generate a big play, Purdy is able to create a little bit of magic.
Or this play from Purdy against the Steelers:
Pittsburgh gets a free rusher coming at him, but Purdy anticipates the pressure, spins away from it and finds Deebo Samuel for a solid gain.
There have even been impressive moments in his past two games, despite some early-game struggles. Moments like this unlikely completion for Jauan Jennings despite heavy pressure in his pocket:
Or even some of what Purdy can do with his legs, like this battle against the Detroit Lions when the defense takes away multiple options and the pocket starts to collapse around him:
Ultimately, if I were asked to plant a flag in the Purdy Discourse, I would probably land right in the middle. He is a very good quarterback who has unlocked parts of Shanahan’s offense that may have been closed off in recent years thanks to his athleticism, ability to create and willingness to be aggressive in the downfield passing game. He also has a lot of talent around him – including a fellow MVP candidate in McCaffrey – and plays for one of the NFL’s best offensive minds.
But if you want to make more of a pro-Purdy case, you certainly have some numbers to back up your argument.
All I know for sure is this: The Purdy Discourse will likely continue long after Super Bowl Sunday.
I mean, if Logan Sargeant thinks so, then you can be pretty sure he does.