49ers grades vs. Cardinals: Fourth-quarter collapses hurt Kyle Shanahan

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GLENDALE, AZ – OCTOBER 28: Cornerback Richard Sherman #25 of the San Francisco 49ers knocks the ball away from wide receiver J.J. Nelson #14 of the Arizona Cardinals during the fourth quarter at State Farm Stadium on October 28, 2018 in Glendale, Arizona. (Photo by Norm Hall/Getty Images) /

Defensive Grades

Over three-plus quarters, the 49ers defense looked sharp enough to thwart any attempts the Cardinals were making to get back into the game. And under most circumstances, allowing 18 points, 321 total yards and forcing two turnovers (three, if you include the first-quarter safety), you’d take it.

But San Francisco played poor situational football, allowing Arizona to go 6-of-14 on third downs over the game.

And those 15 fourth-quarter points by the Cardinals hurt in more ways than one.

Defensive Line

The 49ers’ game plan to limit running back David Johnson worked pretty well, and the interior of San Francisco’s defensive line generated some pressure on Josh Rosen. Defensive tackles Arik Armstead and Ronald Blair each recorded a sack. EDGE Cassius Marsh‘s pressure with the Cardinals backed up against their own goal line resulted in a safety too.

There’s still a serious lack of an edge rush, though, which was glaringly apparent on Arizona’s two fourth-quarter scoring drives.

Grade: B-

GLENDALE, AZ – OCTOBER 28: Linebacker Reuben Foster #56 of the San Francisco 49ers breaks up a pass intended for wide receiver J.J. Nelson #14 of the Arizona Cardinals during the second quarter at State Farm Stadium on October 28, 2018 in Glendale, Arizona. (Photo by Norm Hall/Getty Images) /

Linebacker

Despite Johnson not getting too much going on the ground, the 49ers’ issues with missed tackles continued in Week 8. Rookie linebacker Fred Warner missed one tackle, bringing his season total to nine — second highest on defense behind fellow linebacker Reuben Foster.

Foster was flagged for a defensive pass-interference call while deep in coverage, and that led to a Cardinals field goal. He then suffered a hamstring injury late in the first half. Foster tried to return but couldn’t, being replaced by Elijah Lee.

Lee ended up playing much better than Foster.

Grade: C-

Defensive Back

Rosen ended up targeting cornerback Richard Sherman a few times during the game, who gave up a few catches but ended up finishing with a team-leading seven tackles and one of the three Niners sacks — his first since 2012.

There were modest efforts by the 49ers’ other cornerbacks, Ahkello Witherspoon and K’Waun Williams, too.

Yet the biggest storyline of San Francisco’s fourth-quarter meltdown comes from the back end of the defense. Jimmie Ward got the start at free safety and performed well. So did strong safety Jaquiski Tartt, who recorded the Niners’ second interception of the season — a turnover that eventually led to three points from kicker Robbie Gould.

But Tartt suffered a shoulder injury late in the second quarter and didn’t return. He was replaced by defensive back Antone Exum, who suffered a concussion early in the third. So the 49ers were down to their third-string safety, Tyvis Powell, who allowed Arizona’s fourth-quarter touchdowns.

Depth, anyone?

Grade: C