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How the Bills and Chiefs Found Their Form—and Set Up the Best Divisional-Round Matchup

Two months ago, both offenses were struggling to find the big plays that had defined them both in 2020. Now, though, they’re back on track—and just in time for an all-important game.

Getty Images/Ringer illustration

It’s difficult to get NFL fans to agree on anything, but if you ran a poll asking which divisional-round game people were most excited about, Bills-Chiefs would undoubtedly get most of the votes. Fans love points, and this rematch of last year’s AFC title game figures to be a high-scoring affair. Last weekend alone, Buffalo and Kansas City combined for 89 points in wins that only added to their hype.

But ask NFL fans about this potential matchup two months ago, and it would have elicited a much different response. At that time, these offenses were both in very different places: The Bills had just lost a 41-15 game to the Colts, which came two weeks after a 9-6 loss in Jacksonville, and they ranked 18th in offensive DVOA. The Chiefs, meanwhile, had just beaten the Cowboys, but they scored only 19 points—the fourth time in five games that they had failed to score more than 20.

These two passing games lit the NFL on fire in 2020. But as defenses found coverages that took away the downfield areas that Buffalo and Kansas City both like to attack, they largely got extinguished. That has obviously changed in recent weeks. The Bills have won five in a row and scored at least 27 points in all of those games. And the Chiefs have won 10 of 11 and averaged 36.5 points over their last six games. It took some time, but both offenses finally got back to doing what they did best in 2020: throwing the ball downfield. So how did they do it? And how will these high-powered units match up against their opposing defenses on Sunday?

It’s not a surprise that Buffalo and Kansas City struggled in similar ways this season. They’re awfully similar in how they attack opposing secondaries—using deep crossing routes to stretch the defense both horizontally and vertically. Over the past two seasons, Patrick Mahomes and Josh Allen rank first and second, respectively, in crossing routes thrown, per TruMedia. They do, however, differ in how they get those crossers open. Andy Reid and offensive coordinator Eric Bieniemy pair crossers with a complementary route underneath. Typically, they use Travis Kelce in that role, with Tyreek Hill going across from the opposite side of the field.

Bills offensive coordinator Brian Daboll prefers to use play-action fakes for a similar effect. Allen fakes a handoff, which draws the second-level defenders closer to the line of scrimmage and clears out the throwing window for the crosser.

But, as I alluded to earlier, defenses have gotten better at defending these crossing concepts. Last season, Allen completed 20 crossing routes that traveled 15 or more yards past the line of scrimmage, per TruMedia. He completed eight such passes in 2021. Similarly, Mahomes completed 11 of those crossing routes in 2020 and just four in 2021. To stop those throws, opponents have deployed more Quarters coverage—with four defensive backs playing zone coverage deep downfield—and they’ve had the backside safety pick up those routes. The Packers do that here:

They’ve also used man coverage concepts where a safety assists the receiver’s primary defender and essentially runs a double-team on the crossing route. On this play, the Dolphins secondary works in tandem to deal with two crossing routes heading in opposite directions—a concept Daboll leans on heavily.

With defenses selling out to stop the routes that previously powered these passing games, both the Bills and Chiefs had to change their respective approaches. And they took different paths to get to the same destination.

The Chiefs didn’t really do anything different from a play-calling perspective. Instead, Mahomes started punishing defenses for dropping deeper into coverage by taking easier throws underneath. When in zone coverage, defenses will willingly give up throws under 5 yards. This is known as the “no cover zone.” Here’s Chiefs defensive coordinator Steve Spagnuolo explaining the concept on an episode of NFL Game Pass’s Film Session:

This season, Mahomes, typically a gunslinger who is reluctant to throw checkdowns, set a career high in “no cover zone” completions with 136. This shows up on his passing heat map as well. All that saturated blue in the underneath areas on the 2020 map started to fade away in 2021.

In the past, Mahomes used those underneath routes primarily when he was under pressure. But this season, he’s been more willing to look there from a clean pocket. Per TruMedia, his pressure rate on those completions dropped down to 20.9 percent in 2021. It was at or just over the 25 percent mark in each of the previous two seasons.

Mahomes Is Throwing More Short Passes in 2021

Year Attempts Completions Pressure Rate Time to Throw
Year Attempts Completions Pressure Rate Time to Throw
2018 134 103 31.3% 2.55s
2019 120 86 25.0% 2.51s
2020 150 113 25.3% 2.41s
2021 177 136 20.9% 2.36s

Now that defenses have to respect those routes, more deep routes have opened up down the field, and that’s created a resurgence in the team’s big-play ability.

The Bills, meanwhile, went in a completely different direction to solve their problems. With defenses sitting on the crossers, Buffalo said Fuck it, we’ll just throw it even deeper. The deep crossing routes from 2020 were essentially replaced with post routes. Instead of breaking across the field, Buffalo’s receivers are running their deep in-breakers up the field.

During the 2020 season, Allen did not complete a single post route that traveled at least 20 yards in the air. This season, he completed six, which was tied for the league lead, per TruMedia.

We’ve also seen personnel changes for Buffalo over the past month. The Bills have given more snaps to fullback Reggie Gilliam, who has played at least 20 percent of offensive snaps in three consecutive weeks. (He played over 13 percent of the snaps only one time in the previous nine games, per Pro Football Reference.) That’s helped to diversify the run game—another blocker in the backfield allows Daboll to call more downhill runs—and has made Buffalo’s play-action and downfield passing game more effective.

Buffalo’s Pass Game Has Been Better With Gilliam on the Field

Gilliam On/Off Dropbacks aDOT Yards per attempt
Gilliam On/Off Dropbacks aDOT Yards per attempt
On 41 10.7 8
Off 640 8.1 6.8
Sports Info Solutions

It isn’t surprising that both offenses have figured things out just in time for the playoffs. These coaching staffs and quarterbacks were just too good for their respective slumps to last. Even at their lowest points of the season, it still felt like we’d get another installment of this budding rivalry.

And the Bills are certainly hoping this next one looks a lot like the last, a 38-20 Buffalo win at Arrowhead Stadium in Week 5. That was the first time Allen beat Mahomes head-to-head, and the matchup between the quarterbacks wasn’t particularly close. Both teams were struggling to hit on deep passes at the time, but the Chiefs defense was also slumping and busting coverages at a high rate. Allen was able to take advantage of the unsound defense; Mahomes had a much tougher time against a Buffalo unit that finished the regular season ranked first in DVOA.

Look at that average depth of target! Allen was just launching the ball over the field, and hitting the mark more often than not. He completed five passes over 20 air yards, while Mahomes managed just one.

These teams have changed dramatically since that game back in October, but the goal will remain the same for both: Get receivers open downfield, and get them the ball. How well each defense holds up against these surging offenses could be the deciding factor. On paper, Buffalo would seem to have an advantage there. The Bills finished the season ranked first in both overall defensive DVOA and pass defense DVOA. And while the Chiefs defense has rebounded after a historically bad start, that secondary has been vulnerable over the last month, and the Bills are perfectly capable of exploiting bad coverage.

The question is whether Allen will have one of those games where his accuracy just isn’t there. We pretty much know what to expect out of Mahomes, who has been consistently brilliant during this hot stretch. But if Allen is the quarterback we saw last week against New England, the scoreboard operator is going to have a busy night.

It’s an impossible game to pick, but it’s easy to figure out how it will be won: Whichever quarterback is able to hit on more deep passes will advance to the AFC championship game.