49ers 1st-quarter report card: Offense and defense improving, special teams flop

49ers 1st-quarter grades: Defense

Points allowed: 82 (tied 10th)

First-year defensive coordinator Nick Sorensen is going through some growing pains, which aren't unlike his predecessors, now-New York Jets head coach Robert Saleh and now-Houston Texans head coach Demeco Ryans.

San Francisco thinks highly of Sorensen, so the hope is his defense can jell fully despite dealing with its own rash of injuries, including losing Pro Bowl defensive tackle Javon Hargrave to a season-ending triceps injury

Defensive end Nick Bosa is wreaking havoc on opposing pockets despite notching just three sacks on the season, while linebacker Fred Warner is playing as if he's the top candidate for Defensive Player of the Year.

However, the 49ers' situation at safety has been a revolving door, while the linebacker play behind Warner has been borderline atrocious with Demetrius Flannigan-Fowles and De'Vondre Campbell the primary culprits.

Defensive meltdowns, including ones involving the Niners' linebacker depth, were directly responsible for both losses in Weeks 2 and 3.

If there's one area in which San Francisco needs serious improvement here, it's on third downs where the defense is allowing opponents to convert a whopping 46 percent of third-down tries, seventh worst in the NFL after four weeks.