How Patrick Mahomes, Lamar Jackson and other prolific NFL QBs are changing 4th-down math

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BALTIMORE — The most courageous fourth-down decision of the young NFL season was, in reality, a no-brainer.

The man who made it, John Harbaugh, never doubted it. His Ravens faced a fourth-and-1 in their own territory, with a one-point lead and one minute remaining, and “we were going for it at that point,” Harbaugh said.

Analytics didn’t doubt it either. In fact, a source familiar with the Ravens' staff told Yahoo Sports that Harbaugh "absolutely" knew what the numbers said. Two prominent models, similar to the one the Ravens employ, estimated that going for it upped the Ravens’ win probability by around 17 percentage points. One described the strength of the recommendation in simple terms: “YOU BETTER DO THIS.”

And to many, that robotic confidence fell right in line with the NFL’s nerdiest trend. Coaches went for more fourth-down conversions in Week 1 of 2021 than in any previous single week in NFL history. Behind their aggressiveness are mathematical models that support their courage and suggest that, broadly, they still aren’t being aggressive enough.

There is, though, another undertold story behind that trend, and it was the tale of Harbaugh’s decision Sunday night.

It isn’t just that coaches are adhering to the math; it’s that great offenses, led by great quarterbacks like Patrick Mahomes and Lamar Jackson, are changing the math.

The models don’t exist in vacuums, or in a hypothetical world where every offense and defense is league-average and static. If they did, or if Mahomes and Jackson were league-average, the calculus on Harbaugh’s decision would have been much different.

Chiefs quarterback Patrick Mahomes congratulates Ravens quarterback Lamar Jackson after the Ravens' 36-35 victory Sunday night. (Mark Goldman/Icon Sportswire via Getty Images)
Chiefs quarterback Patrick Mahomes congratulates Ravens quarterback Lamar Jackson after the Ravens' 36-35 victory Sunday night. (Mark Goldman/Icon Sportswire via Getty Images)

In fact, consider that, for much of the 21st century, the league-wide fourth-and-1 conversion rate has hovered in the 65% region. If that had been the Ravens’ success rate, and if the alternative had been to punt the ball back to a mediocre pre-passing boom quarterback, the decision wouldn't have been so obvious. Data analysts hesitate to deal in forged hypotheticals, but below-average offenses and above-average defenses could have reduced it to a toss-up.

A brief dive into the numbers can explain why. Let’s say that the offense, on average, would have taken over at its own 15-yard line, with less than a minute and no timeouts to march into field-goal range. Let’s say that the mediocre quarterback and his mediocre kicker would accomplish that 20% of the time.

Alternatively, let’s say that if the Ravens go for it and fail, turning the ball over on their own 43-yard line, the hypothetical opponent kicks a game-winning field goal 60% of the time.

In that case, depending on the model, a decision to go for it wouldn’t have been worth 17 percentage points of win probability; it might've only been worth one or a few. It might have even cost Harbaugh and the Ravens a percentage point — in other words, punting might've been the optimal decision.

But Jackson and Mahomes, and their prolific QB brethren, change what is optimal.

On one side of the ball, the Ravens' conversion probability wasn’t 65%. It has, instead, been over 80% on fourth-and-1 since Jackson’s first full season as a starter, per Stathead. One model pegged it at 72%. Another, factoring in Kansas City's weak run defense, had it around 85%. A higher success rate tips the scales toward leaving offenses on the field.

And so do opposing offenses. If the Ravens had punted, the Chiefs didn’t have a mere 20% chance to win; they had Mahomes and, therefore, per one model, a 34% chance.

In the modern NFL, offenses move the ball quicker and more freely than ever before. As they’ve improved, field position has become relatively less important, and possession relatively more important. Compared to two decades ago, it matters less where you have the ball, and more that you simply have it.

And that, in a nutshell, is the other reason for the fourth-down craze. Yes, coaches are listening to nerds. But the nerds are also recommending more and more that coaches go on fourth down, because their formulas can quantify the brilliance of Mahomes and Jackson.

Because math and football brains alike know that giving the ball back to Mahomes is a horrid idea.

And because they know that, on fourth-and-1, if the ball is in Jackson’s hands, as the Baltimore star himself said Sunday night: “I feel like we can make anything.”

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