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Film room: Coverage busts by the 49ers defense leads to big plays they’re unable to overcome

The film room looks at the various coverage busts by the defense as well as how the Bills and Josh Allen put on an offensive clinic.

Buffalo Bills v San Francisco 49ers Photo by Ralph Freso/Getty Images

Any plans the 49ers had of slowing down the Bills' offense on Monday night immediately fell apart on the first play of the game when Javon Kinlaw jumped offsides. Three plays later, safety Tarvarius Moore gave up a long catch for 31 yards after a busted assignment. The Bills wouldn’t score on that drive, but it foreshadowed just what kind of night was in store for a defense that yet again needed to shuffle around players due to injuries sustained the previous week.

On the injury front, the 49ers' defense was still without Emmanuel Moseley and K’Waun Williams. In the end, the Bills won comfortably 34-24 thanks to a few key coverage busts on defense throughout the game. Bills Josh Allen threw for 375 yards and four touchdowns. Nick Mullens threw for 316 yards, three touchdowns, and two interceptions.

The 49ers' run game was shut down as well, with the 49ers' offense gaining 87 yards on 21 carries. The 10-point deficit final score felt a lot larger than that throughout the game but all things considered, the game ends 34-31 if Mullens doesn’t throw an interception on the goal line.

Or perhaps they even win if they’re able to punch it in on the opening drive of the game instead of having their 4th down shotgun run stuffed. But that points to a large issue. For the 49ers to win out and even have a shot at the playoffs, they need to win the next four and need to be nearly flawless in those games even to have a shot at winning, and after last night, that might be next to impossible to accomplish. And if it’s going to happen, it needs to be the defense that shoulders the load and plays perfect games. That didn’t happen on Monday night.

Defensive coverage busts

The 49ers busted their coverage on key plays throughout the night and had no answers for the Bills passing game. As mentioned above, the first came on the first drive, and although it did not lead to points, it the first of two of Tarvarius Moore’s coverage busts. He also had one against the Rams in week 12 on a similarly designed play and defensive call.

Week 12, 1st quarter 8:34, 2nd-and-7 at LAR 32

In this clip from Week 12 against the Rams, Moore is aligned as the down safety. The Rams are running a play-action sail concept into the boundary.

The 49ers look to be in a “tuff” cover-3 buzz call with the buzz safety Moore spinning down to the trips side and responsible for carrying anything vertical in his zone. But he gets caught looking in the backfield too long and doesn’t carry the vertical sail route by Robert Woods (No. 17) and gives up a long completion.

Week 13, 1st coverage bust, 1st quarter 13:52, 1st-and-10 at BUF 37

Moore had a similar coverage bust against the Bills on Monday night on the game’s opening drive when he failed to carry the vertical route from wide receiver Cole Beasley.

The 49ers defense has a typical “soft sky” check over the Bills 2x2 formation. “Soft sky” is the Pete Carroll lineage of coaches’ answer to defending four verticals from a single high coverage shell similar to Nick Saban’s rip/liz. Rip/Liz allows Saban to keep eight in the box and still cover four verticals with two overhand defenders, essentially giving them five over four if a team runs four verticals. Soft sky allows the 49ers defense to keep eight in the box and instead uses the deep safety to cover a vertical instead of a second overhang defender.

The Bills run a three verticals concept with two of the verticals coming from the short side of the field, indicating to Moore that he should’ve carried the vertical from the number two receiver Cole Beasley. Instead, Moore flies to the flat and allows Beasley to get down the seam behind him. Allen sees this, rolls left and throws to Beasley wide open.

2nd coverage bust, 4th quarter 9:56, 2nd-and-10 at SF 28

The second time Moore busted a coverage, it directly led to a touchdown and likely put the game out of reach at that point. However, Moore wasn’t the only one who didn’t do their job on this play.

Cornerback Richard Sherman said after the game, “We were in palms coverage, and 2 went to the flat. I adjusted, but we had a few busts on the play. It was unfortunate; they had put us in a look we hadn’t seen, and you know it was a miscommunication down the line, and you can’t have those plays in games like this.”

The 49ers have a fire zone pressure called to the Bills 3x1 formation before the Bills motion to a 2x2 formation. You can see Fred Warner (No. 54) alert the defense to a 2x2 palms cover-2 coverage check when he makes the double fists signal on his head. Cover 2 palms is usually a coverage check used against 3x1.

In palms coverage, the cornerback is reading the number two to number one receiver. If two goes out, the corner stays, and the free safety takes number one. If number two goes vertical, the corner takes number one.

For the safety, the roles are reversed. If two is vertical, the safety takes two man-to-man. If the number two is out, the safety looks for number one and zones off over the top. In the coverage bust, Moore should’ve stayed over the top.

The post-snap reveals that the coverage is mirrored on both sides, palms to the field and boundary. The underneath responsibilities are also mirrored, and it appears the 49ers are running a fire zone pressure underneath the palms coverage. The fire zone indicators are Arik Armstead (No. 91) zoning off and playing a “wall” technique to prevent any in cut from the number two due to having no underneath coverage.

Dre Greenlaw (No. 57) walls off the number two to the boundary side, indicating that the other likely bust on the play is Dontae Johnson (No. 27), who instead traveled with the slot receiver when he should’ve added to the rush with Fred Warner on the right side. That bust likely indicated to Moore that Sherman would be “man on deep” on #1 with Johnson over number 2. As a result, Moore never zones off over number one, and the receiver is wide open for a touchdown.

Brian Daboll scheme’s against 49ers defensive weaknesses

Another coverage bust occurred not so much because of confusion but because a defender allowed himself to get picked by a receiver running diagonally at the snap. It was also a beautifully-designed run-pass option.

3rd coverage bust, 3rd quarter 5:53, 2nd-and-9 at SF 23

Tavarius Moore busted this coverage again. Bills defensive coordinator Brian Daboll also added some nice plays designed to take advantage of the schematic weaknesses of the 49ers scheme, and here he called an RPO designed to take advantage of the crashing weakside defenders. The Chiefs previously ran the play in week 12 against Tamp Bay.

The play is an inside zone RPO designed as an inside zone read run. Except Allen has no intention of running the ball. Instead, he has a tight end slide route off the crashing defensive end and linebacker that is his primary read. Jet motion pulls the flat defender (Moore) out as Moore has to carry his vertical.

Moore gets picked by the slot receivers inside diagonal release upfield instead of going over the top. At the running back mesh point, Allen sees this and, instead of taking the tight end in the flat, elects to go for the big play by lobbing the pass downfield to his wide-open receiver for a touchdown.

Daboll was able to stress coverage weaknesses as well when players didn’t bust.

2nd quarter 14:21, 2nd-and-12 at SF 32

The play call is a play-action dagger concept giving Allen a defined read on a dagger route over the deep seam. Teams don’t often run dagger against 2-high coverage because of how the routes distribute behind the seam-curl-flat (s/c/f) defender and the deep hash safety. But Daboll’s route distribution adds a wheel route from a third receiver.

The wheel route pulls the s/c/f defender out of his position in the seam. Under normal 2x2, he’d likely drop down the seam under 2-high coverage and be in a position to rob the dagger. But the wheel pulls him outside toward the flat and down the sideline so that the dagger route has an open window, thus putting linebacker Fred Warner in a bind. Allen still has to throw a perfect pass over Warner and does so, as the pass is just out of Warner’s reach.

Daboll attacked the schematic weaknesses of the defensive front as well.

2nd quarter 6:14, 2nd-and-2 at SF 34

The play call is just a basic jet fly similar to how the 49ers like to run their Deadpool package with Deebo to the strong side, except the play attacks the weak side wide-5 technique defensive end and leaves the 3-technique defensive tackle unblocked. Thus, it’s a great way to block two defenders to the weak side without a lead blocker.

Allen quickly taps the ball forward to Isaiah McKenzie on the jet fly across the formation, but the defense’s eyes are all on Allen's fake toss action. The 49ers defense had just seen a lot of fly motion after playing the Rams and don’t really focus on that aspect of the play, so it makes sense that they’d disregard the fly on these types of plays.

Thus, the 3-technique Kentavius Street (No. 95) crashes upfield toward the fake toss run action, and Dion Jordan (No. 96) at the right defensive end sets the edge but gets ridden way outside, creating a running lane with no gap support for McKenzie.

In the end, Josh Allen just made plays

At other times, Josh Allen made several plays outside the structure of the play call, and it paid off. Having a quarterback with his mobility and arm strength has been a rough ride since he came into the league in 2018, but the Bills' patience and Daboll’s play designs are finally paying off for the young franchise quarterback.


The defense struggled against a much better offense, and sometimes it’s okay to give the opponent credit. They did everything right, called the right plays, and beat the 49ers' defense's schematic weaknesses. Of course, the game swung on probably three big plays (the two coverage busts above and the Nick Mullens interception at the goal line), but it never felt that close as the Bills were able to at least come away with points on nearly every drive.

The mistakes show that if the 49ers are going to make the playoffs (unrealistic at this point but still statistically probable), they’re going to need to be nearly perfect in every game the rest of the way. Whether that’s possible or not is going to be up to the team to eliminate those mistakes.