49ers report card: Offense bombs while defense deals with a deserter

SANTA CLARA — Here is how the 49ers (6-8) graded in their 12-6 loss to the Los Angeles Rams (8-6) at Levi’s Stadium on Thursday night:

PASS OFFENSE: F

Brock Purdy irrevocably heaved a fourth-quarter pass that was intercepted at the goal line, serving as the offense’s death knell. The 49ers were at the 33-yard line on second-and-10 when Purdy bypassed two wide-open receivers — Ricky Pearsall and Patrick Taylor Jr., both at the 30-yard line — and overthrew Jauan Jennings amid double coverage down the right sideline with five minutes to go. “Something we’ve kind of seen on film. He likes to run curl pumps,” Darious Williams said of his interception.

Jennings caught 2-of-9 targets (31 yards). The 49ers were too intent on forcing Deebo Samuel into a playmaker role after this past week’s gripes about scarce opportunities. That tactic almost paid off, until Samuel dropped a third-quarter pass that may have resulted in the game’s only touchdown. Samuel had just 16 yards on three catches and six targets. Kyle Shanahan also rued another potential big completion, when Purdy underthrew an open Pearsall three snaps before the interception. Fair or not considering the first-half rain, Purdy didn’t help his bad-weather history, completing 14-of-31 for 142 yards, with 61 yards going to team MVP George Kittle.

RUN OFFENSE: D+

Averaging only 3.3 yards per carry is no way to move the ball in a field-goal fight. Credit to Isaac Guerendo for playing through Sunday’s foot sprain and finishing with a 10-yard run on his next-to-last carry; he got stopped for no gain on his final run, preceding the interception. Samuel ran for just 2- and 1-yard gains on his only carries, both in the first-quarter force job. The blocking wasn’t exceptional, aside from the Purdy Plunge for a 3-yard gain on third-and-1 on their final scoring drive.

PASS DEFENSE: C-

The 49ers could have intercepted Matthew Stafford multiple times, including Deommodore Lenoir and Talanoa Hufanga on third-down throws in the first two series. Charvarius Ward allowed a 51-yard catch to Puka Nacau to open the Rams’ go-ahead scoring drive in the fourth quarter; Nacua earlier pinned the ball to the back of Ward’s helmet for an earlier, improbable catch. Stafford was not sacked, but Nick Bosa’s return from a three-game absence helped the front repeatedly pressure Stafford (16-of-27, 160 yards) into overthrows out of bounds. Bosa had three quarterback hits, and Lenoir broke up two passes.

RUN DEFENSE: B

Dre Greenlaw’s season debut was a thrilling ride, in a positive way through three quarters and eight tackles. Then came his exit with leg issues, and De’Vondre Campbell’s subsequent refusal to replace Greenlaw was one of the most treacherous misdeeds in 49ers history. The 49ers already were down a linebacker with Dee Winters’ first-half groin injury, and Fred Warner appeared to aggravate his season-long ankle issue, thus thrusting Demetrius Flannigan-Fowles to play through his own health issues to the bitter end. Kyren Williams ran for 108 yards, including a pair of 9-yard runs through a wilting defense on the Rams’ final scoring drive that ate most of the final 5 precious minutes off the clock.

SPECIAL TEAMS: C

Instead of glaring issues like those that triggered their Week 3 loss at Los Angeles, the 49ers’ special teams were mostly solid, except for a pair of illegal-formation penalties on punts. Jake Moody made both his field-goal attempts, including a 53-yarder amid first-half rain for a 3-0 lead. Deebo Samuel’s kick-return exploits finally kicked in for a 41-yard return in the final seconds, but it was too little too late. Kudos to Jacob Cowing for cleanly fielding and returning five punts (51 yards).

COACHING: D

Four days after a 25-point win, the 49ers were outmatched by the division-rival Rams and essentially ended their playoff pursuit with three games to go. Kyle Shanahan said there was no intention to overcommit to Deebo Samuel, yet it sure seemed like it and that backfired on a very poor offensive day. Shanahan and general manager John Lynch need to reshape and revitalize this roster, staff and front office to make sure they’re back in the playoff hunt in Year 9 as the Niners’ hierarchy. And they have to kick Campbell off the roster as soon as Friday’s transaction wire allows.