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The Bucs’ Defense Dares Opposing Offenses To Pass. So They Do.

The final four playoff quarterbacks may have been born in three different decades, but they do have a few things in common. Their offenses represent four of the top five teams in overall expected points added (EPA) per play and EPA per dropback, according to the nflfastR model, which aligns neatly with the ProFootballFocus claim that we’re still watching four of the top five QBs this season. Passing offense wins championships, as they say, so it’s probably unsurprising that the best passers pass more than you’d expect:

But what do we expect, exactly? Expected pass rate, created and shared publicly by Ben Baldwin, uses situational features like down, distance and scoreline to assess the league-average probability of passing on any given play. We can then measure the amount that teams deviate from that and calculate each team’s pass rate above expectation. It’s notable, for example, that the Kansas City Chiefs and Buffalo Bills are near the top of the league in pass rate considering that they’re often holding onto leads, which is usually when teams run more. So they lead the league in passing more than we’d expect, both on early downs and in general.


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Meanwhile, in the NFC championship game, we can safely assume that Aaron Rodgers and Tom Brady will be slinging it, but there’s an arguably more compelling contrast on the other side of the ball. It’s fair to say that the Tampa Bay Buccaneers are known for their run defense, which has been effective for two years straight. Meanwhile, the Green Bay Packers’ most recent playoff experience before last weekend was having the San Francisco 49ers run all over them.

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Newer defensive metrics like Defenders in the Box Over Expected can help analyze the stylistic differences involved: Tampa defensive coordinator Todd Bowles is much more likely to stack the box and therefore incentivize opposing offenses to pass, while Green Bay defensive coordinator Mike Pettine is more fond of dropping more players into coverage. The Packers actually don’t grade out worst in terms of EPA per rushing attempt this year, but that doesn’t seem to matter to the teams game-planning for them every week. Teams appear to believe that they can run on the Packers and they can’t run on the Bucs, which results in Green Bay facing the lowest pass rate over expectation this year (-5 percentage points), and Tampa facing the highest (+7 percentage points) by a substantial margin when games are competitive.1

These numbers are driven quite a bit by opposing offenses, which vary significantly in terms of how likely they are to pass in general. The Packers played a quarter of their regular-season schedule against the Vikings, Saints and Titans, who are among the top of the league when it comes to establishing the run. Once we account for opposing offenses, we can say that teams are 5 percentage points more likely to pass on any given play versus the Bucs and 2 percentage points less likely to pass on any given play versus the Packers. So, if the Packers follow the lead of other Buccaneers opponents, we can expect to see their already pass-heavy offense get 5 percentage points heavier this weekend. (And perhaps the Chiefs vs. Bills matchup won’t be quite as pass-heavy as we might imagine since, like the Packers, both of those defenses get passed on less than you’d expect.)

Final four NFL playoff team defenses by rank in pass rate over expectation

Team Pass rate over exp.
2 Green Bay -2.4
3 Buffalo -2.2
9 Kansas City -1.1
32 Tampa Bay +5.0

Source: nflfastR

Perception of defensive strengths and weaknesses can be easy to identify at the extremes, but it’s also worth talking about what goes on when defenses seem more balanced. How much did teams pass this season versus, let’s say, the Baltimore Ravens, and why? Is answering this question as simple as figuring out how good teams are at stopping the run versus the pass? In a word: yes.

If you want to pinpoint exactly one variable that explains a large proportion of the variation in pass rate over expectation faced, it would be challenging to do better than rush EPA per attempt. (Seriously, let me know if you can do better.) This is even more effective than rushing yards per attempt, probably because EPA quantifies a lot of the extra stuff that NFL teams implicitly recognize, like how giving up a mere 2 yards is actually a bad outcome on third-and-1.

Here we can see that the Bucs and the Packers (and Bills, and maybe even the Chiefs) face offenses with pretty extreme opposing tendencies, even after accounting for their run defense outcomes, but the directional trend makes sense. Again, general perception and multiyear trends likely matter in all of this. With that said, this is about as clear of a relationship as you’ll find in NFL analytics. And if we include pass EPA per attempt as well, we can account for about half of the total variation in pass rate over expectation faced. All else equal, a standard deviation improvement in pass EPA per attempt for a given defense results in teams passing on it 0.7 percentage points more, and a standard deviation improvement in rush EPA per attempt results in teams passing on that defense 1.4 percentage points less.2 So, teams seem more inclined to change their strategies based on perception and quality of the rushing defense they’re facing.

These numbers give us a bit of color on what to expect this weekend, but it’s also worth considering the roster construction angle here. With (almost) every year, the NFL becomes more of a passing league, and it becomes more clear that passing is, on average, more valuable to team outcomes. The Bucs would certainly rather have their stout run defense than not, but it does come with a downside. Their defense’s ability to stop the run is undisputedly No. 1, but their EPA per pass attempt was worse than the regular-season average, and they face far more dropbacks relative to game state than anyone else right now. They’re likely about to incentivize Aaron Rodgers to do Aaron Rodgers things in significantly more attempts than usual.

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On the other hand, if we considered the expected, rather than actual, pass rates against defenses in the regular season, the Bucs’ defense would have had the ninth-best EPA per play in the NFL, rather than 16th. Meanwhile, the Packers defense ranked seventh in overall EPA per play given up, largely due to their fifth-ranked pass EPA per attempt. And teams will probably continue to run on them, especially on first-and-10, which — as Josh Hermsmeyer has noted — is not exactly a recipe for success.

So we’ve seen what teams do. As for what teams should do, well, that’s still an open question. It definitely makes sense to run more on the Packers than on the Bucs — but how much more? And what’s the ideal pass rate in every single situation? Feel free to take a crack at answering these questions while I watch the games this weekend.

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Footnotes

  1. Periods during any game in which neither team’s win probability is less than 10 percent.

  2. Based on all NFL games played this season, excluding a Week 12 matchup between the Denver Broncos and New Orleans Saints in which the entire Broncos QB unit was out after COVID-19 exposure.

Namita Nandakumar is the senior quantitative analyst for the Seattle Kraken. She previously worked as a quantitative analyst for the Philadelphia Eagles and contributed to The Athletic and Hockey Graphs.

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