Brock Purdy is better than he is given credit for, and the analytics show it

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Wading into the Brock Purdy discourse ahead of Super Bowl LVIII

You know an issue has broken out of the football world and into the mainstream when those who do not engage in the discourse on a daily basis begin to discuss a certain topic.

Such as Brock Purdy.

The Brock Purdy Discourse has dominated the past calendar year, and is set to 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” grew into his role as the starting quarterback for the San Francisco 49ers, the discussion turned from “heartwarming underdog story” to “is he actually a good quarterback, or simply propped up by a creative offensive system while surrounded by a team of Monstars?”

So imagine my surprise when, on Monday, Williams driver Logan Sargeant said this to me and other media members about Purdy during a roundtable in New York City: “You can’t bet against Patrick Mahomes, but I would love to see Brock win just because the underdog story and he gets 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 seem to be setting up as they always do, with the “film watchers” on one side and the “analytical analysts” on the other. Second, the answer(s) to the above questions probably lies somewhere in the middle, a notion we will return to in a moment.

But for the moment, let’s focus on the analytical arguments in Purdy’s favor, of which there are many. At the outset, as someone who spends the bulk of his football analysis in the “film-watching” camp, I do believe it is critical to look at all available bits of data when constructing an argument and coming to a conclusion. The more information you have, the better informed your opinions are.

Let’s start with Expected Points Added, or EPA, a foundation for many analytical arguments. As defined by Pro Football Focus EPA “…is a measure of success which defines the value of each play by the effect it has on the offense’s likelihood to score. For every play, EPA is attributed equally to both teams, and the metric is fairly reliable in identifying the best teams in football. It is common practice to discuss EPA on a per-play basis (EPA / Play), so that the stat is normalized for any disparity in total plays run.”

Specifically, EPA is the difference in the “expected points” before a play, and after. So, if a play is successful, the team will gain EPA, but if the play fails, the team will lose EPA. The metric “is an estimate of how many points a team will score on a drive, given the current situation (Down, Distance, Time Remaining, etc.). Intuitively, as a team gets closer to its opposing end zone, the higher the expected points of the drive.”

With that in mind, we turn to this chart from RBSDM, which charts EPA/Play as well as Completion Percentage over Expected (CPOE), which we will turn to next:

As you can see Purdy, with an EPA/Play of 0.338, led all quarterbacks this season. Dak Prescott ranked second, with an EPA/Play of 0.245.

If you expand the timeframe a bit, and look at 2022 and 2023 combined, 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, comes in second with an EPA/Play of 0.221 for 2022 and 2023 combined.

Now let’s turn to the second metric on this graphic, which is CPOE. Ben Baldwin, the mind behind RBSDM, created a model that outlines the chances a pass will be completed given various factors, including down, distance, yards to go, air yards, and more. That allows you to calculate the “expected completion percentage.” 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 into double coverage.

For this metric, if your expected completion percentage is 70%, and your actual completion percentage is 75%, you have a CPOE of 5%. This number can be negative, for example in 2023 Gardner Minshew had a completion percentage of 65.6%, and an expected completion percentage of 68.9%, for a CPOE of -3.3.

Now let’s return to Purdy and the chart from 2023:

Purdy posted a CPOE of 5.4, which led all quarterbacks in 2023. Josh Allen was second with a CPOE of 5.0. When you expand the timeframe to 2022 and 2023, Purdy clocks in third in this metric with a CPOE of 3.6, behind Geno Smith (4.2) and Jacoby Brissett (3.7).

There is another statistic that can work in Purdy’s favor, which is Adjusted Net Yards per Attempt (ANY/A). This “incorporates passing yardage, sacks, touchdowns, and interceptions. ANY/A is easy to calculate, easy to understand, and has a strong correlation with points scored,” as 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 over 9.00 since Matt Ryan back in 2016, when he won MVP.

Now, 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.” Regarding CPOE, there is a counter that Purdy’s success in that metric is due more to receivers bailing him out than his own play on the field.

Yet, 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 factor, Purdy posted an Intended Air Yards (IAY) of 8.3 this season according to Next Gen Stats, which ranked him 14th in the league.

Mahomes posted an IAY of 6.6 this year, ranking him 40th.

As to the supporting cast argument, an interesting metric debuted this week thanks to E.J. Snyder and Arjun Menon called Quarterback Deficiency Differential or QBDD. Here is Snyder explaining the metric they created:

They aimed to try and quantify how much help a quarterback got from the players around them. The result was QBDD, which they charted here:

Here’s a zoomed-in look at Purdy, in the upper right:

In their findings, Purdy was supported by his surrounding talent, but he still “performed fairly equal to [his] support.”

Again, one more data point, but an interesting one at that.

As always, there will be detractors. Many can — and will — point to Purdy’s performance in playoff games this season and make the case that the 49ers perhaps overcame some subpar play. For example, as charted by PFF, Purdy has three Turnover Worthy Passes (TWP this playoff season, and a TWP% of 3.8%.

Mahomes has yet to throw a turnover-worthy pass, according to PFF’s charting.

So those who doubt Purdy will have their own numbers to point to.

But as noted above, I’m probably someone more aligned in the “film watchers” camp, so there are some arguments to be made in Purdy’s favor there as well. Arguments and examples of Purdy perhaps doing more in the 49ers offense than his predecessors, and creating opportunities for San Francisco beyond the structure of the offense. This is something I highlighted earlier in the season, when San Francisco and Purdy carved up the Pittsburgh Steelers.

Plays like this one stand out, where Purdy makes a quick reaction to T.J. Watt dropping into the throwing lane and gets to a “Plan B:”

Purdy not only makes the initial “no-throw decision” by pulling the ball down and avoiding an interception thrown directly to Watt, but he gets his eyes back to the left, picking up Christian McCaffrey on a quick slant route. The play goes for just a seven-yard gain, but on a snap where the defense had everything in place to generate a big play, Purdy is able to create a tiny bit of magic.

Or this play from Purdy against the Steelers:

Pittsburgh gets a free rusher on him, but Purdy anticipates the pressure, spins away from it, and finds Deebo Samuel for a solid gain.

There were even impressive moments over his past two games, despite some of the early-game struggles. Moments like this improbable completion to Jauan Jennings, in the face of heavy pressure in the pocket:

Or even some of what Purdy is able to do with his legs, like this scramble against the Detroit Lions when the defense takes away multiple options, and the pocket starts to collapse around him:

Ultimately, if asked to plant a flag in the Purdy Discourse, I would come down probably right in the middle. He is a very good quarterback who has unlocked parts of Shanahan’s offense that might have been closed in recent years thanks to his athleticism, ability to create, and willingness to be aggressive in the downfield passing game. He also does have 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 wanted to make more of a pro-Purdy case, you certainly have some numbers to bolster your argument.

All I do know for sure is this: The Purdy Discourse is going to continue probably long after Super Bowl Sunday.

I mean, if Logan Sargeant thinks it will, then you can be pretty sure it will.