Let's jump in a time machine back to 2015 -- Sept. 29, 2015 to be exact, the day after a Packers win over the Chiefs on Monday Night Football.

In that contest, Aaron Rodgers completed 24 of 35 passes for 335 yards with five touchdowns and no interceptions en route to Green Bay's 38-28 victory. 

Relatively new-on-the-scene football analytics website Pro Football Focus (PFF) gave Rodgers' performance an overall grade of -0.8, the 16th-highest among all quarterbacks that week. That -0.8 equates to a PFF grade of 67.0 today. 

When that PFF grade dropped, it left NFL Twitter's collective mouth agape. How in the world did Rodgers, who threw for 335 yards and completed nearly 70% of his passes with five touchdowns (!) and no interceptions earn a grade in the negatives! Ri-dic-u-lous was the general consensus. 

The backlash was so rampant, Ben Stockwell, who still works at PFF as head of data collection, wrote an article that day defending (see: explaining) the justification for Rodgers' average grade. 

In it, Stockwell pinpointed a fumble by Rodgers and a dropped interception by a Chiefs defender as the key grade-lowering components while mentioning three of Rodgers' five scores came on "expected" throws in which his wideouts did the heavy lifting to morph those plays from simple completions to touchdowns. 

As someone who'd instantly taken a liking to PFF's overarching idea and gravitated toward and agreed with its granular approach to analyzing football, this Rodgers grading controversy felt like what should've been a watershed moment. After reading Stockwell's piece, PFF's stance felt unshakeable. The rationale made perfect sense. And while it swayed the opinions of many, not everyone was convinced.

The point of this story isn't to insinuate that I viewed then or currently view PFF grades as gospel. It's meant to advocate for what PFF pushed to the forefront of football analysis -- evaluating players by distilling what each did individually on a given play. 

Because now, eight years after that -- maybe only to me -- fateful late September Tuesday, we're still in the throes of a heated, widespread debate on how to properly evaluate quarterbacks. Except this time, it's not a former first-round, future Hall of Fame passer at the center of the discussion. It's last year's "Mr. Irrelevant," who's not so irrelevant anymore, 49ers quarterback Brock Purdy. 

Purdy's the NFL's current leader in some signature categories -- quarterback rating (123.1) and touchdown-to-interception ratio (9:0). He trails only Tua Tagovailoa in yards per attempt (9.7 to 9.3) and is second in completion percentage at 72.1%. Despite all that, there are plenty of analysts -- including myself -- who aren't overly enamored with Purdy himself as a passer. Kyle Shanahan's brilliant play-designing talent coupled with an embarrassment of riches at receiver, tight end, and along the offensive line are cited as the main drivers of the absolute wagon that is the 49ers offense. 

Actually, I shouldn't write I'm not enamored with Purdy. It's more correct to say, like Rodgers on three of those touchdown passes in 2015, Purdy is mostly operating "as we would expect" any starting quarterback to given what has been presented to him within San Francisco's attack. 

And the results that materialize from a quarterback playing "as expected" hinge on the offensive environment. It's when a quarterback functions either "below" or "above" the scheme that they should be subject to negative or positive marks on their evaluation. 

How we view quarterbacks is kind of a catch 22. Quarterback is accepted as the most important position on the field, but a quarterback's statistics are very much contingent upon the performance of teammates.

For example, during the 2022 regular season, the 49ers averaged the most yards after the catch per reception (6.62) in football. Entering Week 6, they're fourth in that category at 5.71 yards. Of course, leading a wideout (or failing to do so) can impact YAC, but in general, what pass catchers do with the ball in their hands is completely out of the quarterback's control. 

Purdy's Big-Time Throw rate (the highest degree of difficulty throws with the highest value) of 2.0% in 2022 was not only very low, it was lower than his Turnover-Worthy Play rate of 2.7%. Credit to Purdy -- thus far in 2023, he's increased his BTT rate to 4.7% and his TWP rate has only slightly increased to 3.1%. Both rank in the Top 15 in each category, which is damn respectable but shouldn't incite serious MVP consideration as the raw numbers would strongly suggest. 

(On this note, I'm acknowledging there's nothing Purdy can do about his current luxurious situation, and he's cooking in it. And Shanahan has clearly proven he can win without a freakazoid at quarterback.)

NFL fans are smarter today about the nuances of the game than at any other point in football history. We can thank technological and analytical advancements, and social media provides an enormous platform to disseminate those advancements to a larger audience than ever before.

We know sacks aren't the only way to measure a pass rusher's production. We know throwing the football is more efficient than running the football. We know wins aren't a quarterback stat. 

What should come next is widespread acceptance that not every big statistical game from a quarterback automatically means that quarterback played at an elite level. Now, of course, a passer can "win" with his mind by finding the open receiver in a flash or rapidly moving through his reads to get to the third or fourth target in his progression. And Purdy seemingly does those things well. 

(If the name TOM BRADY is flashing in your mind right now as the gold-standard of mental dominance at quarterback you're onto something. Brady was a remarkable processor and surgically accurate. But, vitally, Brady also lit up the Big-Time Throw scoreboard, with 10 seasons with a BTT rate higher than 5.0%. In all but two of those seasons, his TWP rate was lower than 2.0%.)

But with how quickly defenders get to the quarterback today and how fast cornerbacks close throwing windows, every offensive coordinator attempts to "scheme" a pass catcher open on the quarterback's first read. And more than ever, that first read is a short, naturally high-percentage throw. 

Per PFF, the median for first-read throws league-wide currently sits at 67%, and Purdy has the fifth-highest first-read throw rate at 73%. 

If a receiver is "schemed open" or simply uses athleticism to separate, and the quarterback throws accurately to him, it can't be viewed as a special play made by the passer. Those plays are expected.

And the vast majority of throws each game for all quarterbacks -- not just Purdy -- are "as expected." It's the errant toss behind a wideout on a shallow cross, the perfectly placed pass on a vertical down the sideline over the corner and in front of the safety, or the late throw over the middle into traffic that separate the bad from the good, the good from the great, and the great from the elite at the quarterback position.