49ers film room: Breaking down Brock Purdy’s game-sealing interception

The interception isn’t on Purdy. Quarterbacks can’t anticipate free rushers when there aren’t supposed to be any free rushers and other players have jobs to do.

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The 49ers entered the game already eliminated from the playoffs as both the Commanders and Rams won, putting the 49ers out of reach of a wildcard spot. The team likely knew this as they took the field for kickoff but they didn’t play any differently.

Unfortunately, when the dust settled, they looked like the same team they have all season: a mistake-prone offense failing to score enough points and a beat up defense doing its part to keep them in the game until collapsing late. The 49ers left Miami with a loss 29-17.

The nail in the coffin in this one was a Brock Purdy interception out of the two-minute warning. The 49ers were driving to make a comeback down 22-17 and needing a touchdown.

On 1st-and-10, Purdy was hit as stepped up into the pocket by a late free rusher and the pass fell short and was intercepted by Miami nickel defender Kader Kohou. Had Purdy not been hit, one could argue either way if the pass would’ve been completed or not. Regardless, it’s worth looking at what exactly happened.

Situation: 4Q, 1st and 10 @ SF 47, 2:00 remaining

The 49ers came out of the 2-minute warning with a play call to beat Tampa-2 coverage they surely knew they would get. Miami had played a fair bit of it throughout the game and Kyle Shanahan called up a staple passing concept that stresses that particular coverage and could be a big play.

The play call was a 3x1 dagger concept designed to put stress on the nickel defender with a high-low read. The design has Jennings running the dagger route, Deebo motioning into the slot to run the seam route, and Kittle running a return route underneath the dagger.

The Dolphins have a disguised Tampa-2 coverage rotation post snap and are showing single high cover-1 defense pre-snap with the corners in press technique man to man.

Dagger is a good concept to beat Tampa-2 coverage from a 3x1 formation because the nickel strong hook/curl defender is put into conflict with the route from Kittle underneath and the dagger route behind him.

It usually takes some kind of super athletic play from hook or middle run through defender to make a play on the dig and most defenses do not have a player who can erase the dig that way.

Kohou, as the nickel defender here to the pass strength, is coached to be alert to the “wrap” concept (dagger) and feels the dagger route while keeping vision on the quarterback and reading Purdy’s eyes. The seam route, or “deep thru” route, pulls the middle run-through defender out of the middle of the field.

He doesn’t bite on the shallow return route from Kittle and keeps gaining depth. For this reason, I have doubts that Purdy would have completed this pass from a clean pocket based on the way Kohou was drifting upfield and into the dagger window.

Based on previous experience with Purdy throwing dagger concepts over the middle of the field, a layered throw with a nickel defender zone matching the dagger would’ve been extremely difficult. He’s thrown multiple interceptions while trying to “layer” throws over the middle too. So it’s not a given that he would hit this throw if given the chance.

For example, in the play above from week 5 of 2023, notice the Cowboys nickel defender squatting on the short curl route from Kittle, effectively opening the zone for Deebo on the dagger route deep behind him. He’s flat-footed and can’t recover to affect the throw. Purdy is nails on layered throws.

But throws with the defender squeezing the window are much more difficult. Can he make the throw? Sure. It would’ve ensured a $55 million contract. Unfortunately that did not happen and we’ll never really know. The interception isn’t on Purdy. Quarterbacks can’t anticipate free rushers when there aren’t supposed to be any free rushers.

How the pass protection and pass rush fit into the play

Calais Campbell (No. 93) landed the eventual hit on Purdy that caused the pass to fall short but it was made possible by the defensive line stunt and Dolphins defensive end Zach Sieler (No. 91).

Here, Dolphins lined up on first down with two defensive ends in the interior rushing from the defensive tackle positions, Campbell and Sieler, and went with two outside linebacker pass rush specialists on the edges, Emmanuel Ogbah (No. 44) and Chop Robinson (No. 91). They’re running a “tackle/tackle” stunt.

Sielier, as the 2i-technique defensive tackle will rush the A-gap to his left and pin both the left guard Nick Zakelj and center Jake Brendel inside while Campbell rushes the opposite A-gap and then will loop around inside.

The 49ers are in “300 Jet” pass protection, a 4-man slide to the right blocking down to the two widest with “big on big” (offensive line on defensive line) and “back on backer” with the protection back, Patrick Taylor looking for blitz or rush threats from the inside out.

The stunt is based on the center pass protection declaration. Whichever way Brendel declares the slide, the looper will peel around the opposite way. Brendel set the protection to block four down to the two widest and most dangerous on their right side. The TV broadcast didn’t pick it up, but likely when Brendel did this, the Dolphins defense declared their rush.

Defenses across the NFL know how and where to bait offensive lines and get them to slide protection. We see this often with defensive coordinators manipulating the protection and bringing back side pressure away from the slide.

The protection slides to the right. Sieler spikes the A-gap from the 2i position and the four offensive linemen cave to that side. Sieler is driving up field into Brendel and Zakelj as Campbell peels off the rush and loops inside.

The pressure off the edge forces Purdy to step up but no big deal right? Colton McKivitz gets beat off the edge but recovers well enough to keep Purdy clean. But the pressure forced him to step up into Campbell’s rush. Campbell hit Purdy as he threw.

The offensive line had a protection bust in picking up the stunt but Taylor is also partly responsible for the free hitter on Purdy too. He released too quickly from the backfield, did not appear to scan for threats, and should have probably picked up Campbell, whom he would have seen if he had slowed down his release to read the front.

The protection issues this season bit the 49ers at the worst times. I have written about these before when I detailed what hot routes in the Shanahan offense look like. This isn’t really an issue on this particular play that Purdy could mitigate. There simply wasn’t enough time for him to do anything other than what he did. And having the ability to reset the protection wouldn’t have mattered here.

Sometimes you just tip your cap to the defense. It’s not easy for an offensive line to disengage pass rushers like that and slide to pick up a loop stunt and free rusher. That’s why the running back is in pass protection as well. And that’s why defenses do it to the line slide. And the 49ers paid for it, adding insult to injury on a day when they were officially eliminated from the playoffs.