The San Francisco 49ers saw the Seattle Seahawks win Super Bowl LX on their home field on Sunday, marking the end of the 2025 NFL season. It wasn’t expected to be a Super Bowl contending year for a 49ers team that shed several veteran salaries in the offseason, while letting other key free agents walk.

But San Francisco had an impressive season, pushing through to the playoffs with a strong second half of the year and even stealing a playoff game on the road against the Philadelphia Eagles before their season came to an end against Seattle in ugly fashion.

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The Seahawks ultimately hoisted the Lombardi Trophy on Sunday, and they did so behind another elite performance from their vaunted defense. Over the past two seasons, we’ve seen the elite quarterbacks fall short against more complete teams in the playoffs. Last year, it was Patrick Mahomes to the Philadelphia Eagles in the Super Bowl. This year, Matthew Stafford and Josh Allen both fell short against elite defenses (albeit in some amazing games), and arguably the best defense in the NFL won the Super Bowl with the Seahawks.

While teams need to certainly be strong at a top-10 level on both sides of the ball, we’re starting to see a big trend emerge in the NFL: you need to win with four to win football games. With how much offenses have evolved over the years, having an elite defense has become even more important in today’s NFL.

When the 49ers went on their deep playoff runs, those elite Kyle Shanahan offenses were boosted by top-tier defenses usually built off a strong defensive line. San Francisco certainly had one of those in 2019 with the group of Dee Ford, Nick Bosa, Arik Armstead, and DeForest Buckner. The 2021 group had a good trio with Armstead, Bosa, and D.J. Jones, as well as a committee of other defensive linemen that fit well as complementary pieces (Charles Omenihu, Arden Key, Samson Ebukam).

In 2022, that group was much of the same, while the 49ers added Javon Hargrave, Randy Gregory, and Chase Brown in 2023 when they returned to the Super Bowl. San Francisco did put more resources towards their secondary (signing Charvarius Ward, draft picks, etc.) over the last few years, but a strong defensive line was always paramount to success on that side of the ball.

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When you look at the top contenders in 2025, almost all of them have top-tier defensive lines. In the NFC, Seattle had an elite defensive front with top-tier interior defensive linemen who were difficult matchups for the 49ers and quality edges with experience. Then, there was the Rams, who have a strong group with Jared Verse, Kobie Turner, Poona Ford, and Braden Fiske.

In the AFC, the Denver Broncos had a great front with All-Pro Zach Allen, Pro Bowler Nik Bonnito, D.J. Jones, Jonathan Cooper, and John Franklin-Myers. The Patriots were a great defensive unit this year as well, while the Texans had Will Anderson and Danielle Hunter off the edges to go with Sheldon Rankins on the interior.

Winning with four is so paramount in today’s NFL because it allows defensive playcallers to be more creative with their coverage schemes and limit the chances for explosives for these opposing offenses. Mike Macdonald and the Seahawks were so successful this year because they stopped the run at an elite level without needing extra defenders at the line of scrimmage. That made the blitz packages so much more effective, but Seattle also regularly won with four rushing the passer.

The 49ers have a bit to go to get that vaunted defensive line back. Nick Bosa is the key piece, and he’ll be welcomed back after missing much of the season with a torn ACL. Rookie first-round pick Mykel Williams missed out on crucial reps after tearing his ACL halfway through the year, and his development in Year 2 will be key. On the interior, rookies Alfred Collins and C.J. West proved they could be rotational pieces going forward. But it feels like the 49ers are still missing one key guy on the interior.

If they can retool their defensive line to be the key to the defense this offseason, the 49ers will be in a great spot for contention in 2026. Perhaps the draft can help with that.