The 49ers’ defense looked absolutely dominant to start the 2025 season, and then injuries basically ruined everything. In just the first two weeks, when the team was mostly healthy, they held the eventual Super Bowl champion Seattle Seahawks and New Orleans Saints to historically bad offensive performances. Their defensive output during those games would’ve ranked first in the entire NFL if sustained over a full season, that’s how good they looked.

But then Nick Bosa went down in Week 3, Fred Warner got hurt in Week 6, and the whole thing fell apart. Mykel Williams, the promising 21-year-old drafted to energize the defensive line, tore his ACL in Week 9. By the end of the season, the defense had completely cratered, finishing with a league-low 20 sacks and ranking 25th in defensive efficiency. Those numbers don’t reflect what this unit is actually capable of, and that’s what makes the injuries so frustrating.

The impact Williams had in just nine games tells you everything about what the team lost. Before his ACL tear, the 49ers ranked sixth in run defense efficiency. After he went on injured reserve? They plummeted to 26th. Double that with losing Bosa, and suddenly the entire defensive scheme broke down. The run defense got shredded, which meant the unit couldn’t get off the field on early downs, leaving pass rushers exhausted and ineffective on obvious passing situations.

GM John Lynch called guys like Bosa and Williams “force multipliers”, players who make everyone around them better. Williams was just catching on when he got hurt, constantly drawing double teams and freeing up teammates to attack the quarterback. That kind of impact shouldn’t be underestimated.

The good news? Both Bosa and Williams are expected back for training camp in 2026. The front office has also made some aggressive moves, trading for defensive tackle Osa Odighizuwa, who had 52 pressures last season alone, nearly as many as all the 49ers’ defensive tackles combined. Second-year players Alfred Collins and CJ West, drafted specifically to develop into pass-rushing threats, should improve significantly under new defensive coordinator Raheem Morris.

There’s still work to do. Bryce Huff, a key edge rusher, retired last month, and the team is exploring adding veteran help. Nick Bosa’s brother Joey is someone they’ve discussed, though his price tag remains steep.

If the 49ers can keep their defensive line healthy and allow the scheme to function as intended, with specialized players handling their assigned roles instead of being forced into emergency situations, this could be one of the league’s elite defenses. The first two games of last season proved that. Now it’s all about staying on the field.