QB Supporting Casts: Part I
Who's really done more with less?
There is likely no greater challenge in the evaluation of quarterbacks than separating the signal caller from his teammates. And let’s be real, it’s impossible to do in an absolute sense. But that doesn’t mean we can’t try! In this study I will be using PFF grades to estimate the strength of each team’s pass catching and pass blocking going back to 2006.
My first attempt was the easy, lazy method - take the receiving and pass blocking grades for each team, average them, and call that averaged grade a proxy for offensive supporting cast. Unfortunately, it ended up being a bit more complicated than that.
First of all, the grades are not scaled the same way from one season to the next. League average receiving grades fluctuate between 68 and 76, while league average pass blocking grades have a ridiculous range of 63 to 83. I don’t know if PFF has changed their methods or scaling at various points in their history, and/or receiving and blocking proficiency have genuinely varied that much from season to season. Whatever the reason (which we’ll probably never know), it was clear that I’d have to normalize the grading scale across the 2006-2023 database. Luckily, this adjustment was easy as I simply converted grades into z-scores.
The second problem I ran into was the apparent correlation between passing and receiving grades. One hand, it’s common sense that a QB delivering accurate, on-time passes will help his receivers make more plays. But I naively thought that PFF accounted for this in their film based grading. And maybe they try, but it’s damn near impossible to grade receivers completely independently from the quality of passes that come their way. As it turns out, the r^2 between passing and receiving grades is exactly .50, which means a full half of the variance in receiving grades can be explained by the quarterbacks they played with. An annoying development for this study, but not insurmountable.
I suspected a similar issue might plague the blocking grades, but fortunately those seem to be much more independent from the QB’s involved. Since there’s no PFF grade for sack avoidance, I used team sack rate as a proxy to see if it correlates with pass blocking grades. The r^2 here is only .12 which means only a very minor adjustment is called for.
To deal with the passing/receiving collinearity, I decided to subtract half of each team’s z-score for passing grade from its z-score for receiving grade. Since the r^2 between the two is .50 it makes sense to incorporate passing grades at half weight into receiving grades. For example, the 2023 Dolphins had a passing z-score of 1.50 and a receiving z-score of 2.10. I took 1.50 x .5 and subtracted it from 2.10 for an adjusted receiving z-score of 1.34 after rounding. In practical terms, this means Miami had elite receivers whose grade was inflated even more by very good QB play. I then did a similar adjustment for blocking grades by subtracting sack rate z-scores x .12 from pass blocking z-scores.
Now that we have receiving and pass blocking grades are converted to z-scores and adjusted for collinear effects, a much clearer picture begins to emerge as to which teams had the strongest offensive supporting casts:
The table is set by default to rank teams by receiving support but is also sortable by pass blocking support, yearly rankings, and team by team.
As much as I love data, I will not publish any statistical study unless it passes the smell test. This, in my opinion, clearly does. Three of the top five receiving teams since 2006 have been the 2021-23 San Francisco 49ers, which should come as no surprise to anyone who regularly follows the NFL. It’s worth noting that PFF receiving grades are obviously influenced by scheme and the ability of coaches to design plays that get receivers open. For this particular study, I consider that a feature rather than a bug because from a quarterback’s perspective, it doesn’t matter why his receivers are open. While the Niners have had a loaded offensive roster for a few years, they probably wouldn’t sit atop this list if not for the genius scheming of Kyle Shanahan.
The worst receiving team by a mile was the 2015 Eagles, highlighted by a preposterous 46 drops and Nelson Agholor famously being dissed by a Philadelphia firefighter. The 2006 Patriots were well known for having terrible receivers and that reputation is backed up by the data (but remember we’re only looking at offensive support here, so let’s not get into QB wins territory, please).
I’d say the blocking numbers also pass the smell test, though I was not expecting a Browns squad of all teams to top this list. In retrospect, Baker Mayfield’s alleged 2020 breakout season was heavily aided by having all freaking day to hold the ball and get away with it. One thing that stands out is Green Bay consistently putting Aaron Rodgers behind elite pass blocking lines, which in my opinion makes his proclivity to take sacks and throw the ball away even more troubling.
In the cellar we find the 2019 Dolphins, who coach Brian Flores later accused of trying to lose on purpose via bribes from ownership. But the more interesting pattern near the bottom is the presence of the Arizona Cardinals franchise. The Cards occupy 7 of the worst 16 pass blocking units of the PFF era! And the amazing thing is that these seasons weren’t consecutive but spread out over a decade-and-a-half and several coaching and front offices regimes. How can one franchise be this consistently awful at drafting and developing a single unit?
In Part II of this study we’ll be analyzing offensive support as a whole and what it means for the perceptions of various quarterbacks. Stay tuned!