For the 49ers to improve on their run to the divisional round of the playoffs last season and truly contend for the Super Bowl in 2026, there needs to be a stark improvement on defense.
Under Robert Saleh last season, the defense was able to close out games with key stops but, with injuries removing defensive cornerstones from the equation, the overall performance was sub-par.
Indeed, the 49er defense finished the season 24th in EPA per play allowed, and a dismal 3oth in success rate.
In other words,
the 49ers regularly gave up explosive players and, more often than not, allowed opponents to gain the required yardage for a successful play on a given down.
That simply must change this season and, with training camp on the horizon, there are three players who go into the year under considerable pressure to deliver, as their performances will have a huge influence on how the defense fares under new coordinator Raheem Morris in 2026.
DE Mykel Williams
It is unclear whether Williams, who fell victim to the infamous MetLife Stadium turf in tearing his ACL in Week 9 of his rookie season, will be ready for Week 1 of the 2026 campaign.
Still, the lack of a veteran signing at defensive end suggests the 49ers are betting on Williams bouncing back from that injury and enjoying a breakout Year 2.
Williams displayed decent promise as a rookie before his injury. He commanded attention as a pass rusher, drawing attention from multiple linemen and displaying his prowess as a pocket pusher, though his strength was in his play against the run.
Posting four tackles for loss in his debut season, Williams’ average depth of tackle against the run was minus 0.1 yards, per PFF, illustrating his ability to win the leverage battle with opposing offensive linemen and make plays at or behind the line of scrimmage.
When he is cleared, the 49ers will want Williams to display continued development in both areas. With little in terms of insurance should he fail to do so, there is substantial pressure on the former 11th overall pick to live up to his draft status in 2026.
LB Dre Greenlaw
The signing of Greenlaw to reunite Fred Warner with his longtime running mate at linebacker was one of the feel-good moves of free agency, and it made perfect sense.
San Francisco’s defense was at its brilliant best with Warner and Greenlaw patrolling the middle of the field, something they have not done together since the Super Bowl defeat to the Kansas City Chiefs in which the latter suffered his devastating Achilles injury.
While there were signs of promise from the now-departed Dee Winters, the Niners never truly managed to fill the Greenlaw void in 2024, when he spent most of the season on the shelf, or in 2025 following his departure for the Denver Broncos.
The question for Greenlaw, following his sojourn in Denver, is whether he can have the same level of impact as he had prior to his injury. With the 49ers lacking experienced options behind him and Warner, it is vital for this defense’s hopes of success that he does so.
S Malik Mustapha
The 49ers added some veteran insurance at safety in the form of Ashtyn Davis, but the onus remains on the young players in whom they have invested draft capital to emerge.
Ji’Ayir Brown will be keen to prove his worth in a contract year, but the player are likely counting on the most at safety is Mustapha.
Limited to 12 regular-season games last season as he recovered from a torn ACL suffered in Week 18 of 2024, Mustapha endured something of a sophomore slump, allowing a completion rate of 66.7%, up from 35% as a rookie, and a passer rating when targeted of 116.9. In 2024, that number had been an impressive 44.4.
With his yards per target allowed ballooning from 4.2 in 2024 to an even 10 in 2025, Mustapha needs a strong training camp to put himself in position for a return to his rookie form.
At his best, Mustapha has the instincts and athletic ability to excel in coverage, while his aggressive in pursuit and physicality against the run make him an ideal fit for this defense.
The 49ers can’t afford the safety position to continue to be a deficiency in 2026, and a resurgence from Mustapha is key to them solidifying that spot.
