The 7 Biggest Takeaways From the 49ers' Loss Against the Seahawks

So much hype was built for the San Francisco 49ers going into their Week 18 matchup with the Seattle Seahawks.

Unfortunately, the 49ers couldn't match the hype. Their six-game winning streak came to an end against the Seahawks, losing 13-3. They will not win the division or be the No. 1 seed in the NFC.

The 49ers will either be the No. 5 or the No. 6 seed, depending on the Los Angeles Rams losing or winning this week. Let's dive into the seven biggest takeaways of the 49ers' loss to the Seahawks.

49ers run defense

The mediocre 49ers' run defense showed its ugly head tonight. It was clear the game was going to be a long one for them after the first quarter, when they allowed 88 yards. They finished the game with 180 yards allowed.

They were a significant reason the 49ers lost this game to the Seahawks. Robert Saleh couldn't find the right formula to keep Kenneth Walker and Zach Charbonnet bottled up.

And when he did, his players failed him. This has to be the most tackles missed from the 49ers this year, and probably the most in years. What a brutal showing.

3rd-and-17 run allowed was the dagger

Jan 3, 2026; Santa Clara, California, USA; Seattle Seahawks running back Kenneth Walker III (9) rushes the ball against the San Francisco 49ers during the first half at Levi's Stadium. Mandatory Credit: Neville E. Guard-Imagn Images | Neville E. Guard-Imagn Images

The cherry on top for the 49ers' atrocious run defense came in the fourth quarter when they allowed a conversion on 3rd-and-17. Seattle ran a shotgun sweep play to Walker.

That's usually a play where the offensive coordinator is waving the white flag. Converting on 17 yards on any down is extremely difficult. Yet, the Seahawks made it look easy.

The 49ers' defense couldn't make a tackle to save their lives. As a result, it didn't save the chances for them to win the game and was the dagger.

Malik Mustapha and Ji'Ayir Brown woes

This is becoming routine to mention Malik Mustapaha, and especially Ji'Ayir Brown, as a negative from the game. They are completely useless.

Both are inept in pass coverage and get lost as run defenders. Look no further than the first touchdown allowed. Brown let himself be erased by a backup tight end so easily.

It freed up Zach Charbonnet to the second level and forced a one-on-one with Mustapha. He would whiff badly tackling Charbonnet and give the easy touchdown to him. It should've been stopped.

What a terrible duo. It's been an issue all year long since the 49ers began starting them. The offseason needs an emphasis on adding a player or two at the safety position.

Brock Purdy rude awakening

Brock Purdy wasn't bad in this game, but he certainly wasn't great. His performance against the Seahawks is a far cry from how he's looked in the last four games.

The reason for that is Purdy wasn't allowed to hold onto the ball for as long as he had in the last four games. He needed to get the ball out of his hands promptly.

Instead, he had a handful of plays where he held on too long and got pressure in his face and was sacked. This was a rude awakening for him that he was playing against an actually great defense for once.

Amnesia to the running game

Christian McCaffrey has been electric in the last few games, but Kyle Shanahan treated him like a third-string player. A whopping three hand offs is all McCaffrey received in the first half.

Now, the Seahawks do have a good run defense. But to give zero effort in establishing the run in the first half is wild, especially since McCaffrey has been running extremely well.

Mike Macdonald schools Kyle Shanahan

For most of this game, Seahawks coach Mike Macdonald, who calls the defensive plays, schooled Shanahan. This isn't the first time this has happened.

It last occurred two years ago when the 49ers played the Baltimore Ravens on Christmas, when Macdonald was the defensive coordinator. He has Shanahan's number in primetime at Levi's Stadium.

49ers will not make the Super Bowl

Even if the 49ers clinched the No. 1 seed, they probably weren't going to the Super Bowl. Their defense is just a bunch of bodies out there playing football with nothing noteworthy.

There is only so much Saleh can do when his star players are out for the year. The 49ers' offense isn't going to be able to carry the load, as they proved in this game.

It means their season would've crumbled thanks to the defense soon. This is a season that the 49ers have been playing with free money, so any win after this will remain unreal.

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