SANTA CLARA – The San Francisco 49ers just lost again to the Kansas City Chiefs, this time 28-18. Here are the 49ers' grades for this embarrassing performance.

QUARTERBACK: F

This was the worst performance of Brock Purdy's career. He was 17 of 31 passing for 212 yards, 1 touchdown run, 3 interceptions and a grotesque quarterback rating of 36.7. To be fair, Deebo Samuel missed most of the game with illness and Brandon Aiyuk left the game with what the 49ers fear was a torn ACL, so Purdy didn't have many open receivers. Still, at least two of the interceptions were his fault. One was a missed throw and one was forced into a double coverage in the end zone. Once again, Purdy tried to be Superman when he was just Clark Kent. After the game, Shanahan Purdy lectured the media at his locker for five minutes. Purdy stared at Shanahan silently and nodded, then they hugged and Shanahan walked away. I asked Purdy about the nature of the conversation. “We talked about some things throughout the game, just some moments and how we can get better in the future.” Sounds like Shanahan is giving him a makeover for his mistakes. Purdy looked anything but a franchise quarterback this season. He is one of the main reasons the 49ers lost four games.

RUNNING BACKS: C

Jordan Mason gained just 58 yards on 14 carries against a great run defense. He's an incredibly tough runner, but he doesn't have a lot of skill to his game – he just throws himself into the offensive line as hard as he can. Unlike Chiefs running back Kareem Hunt, who has a nice jump step and cut. Isaac Guerendo carried the ball once, gained two yards and fumbled the ball out of bounds.

Full-back: D

39 carries, 14 rushing yards and zero catches on 3 targets.

WIDTH RECEIVER: D-PLUS

Brandon Aiyuk dropped a potential long pass before leaving the game with a torn ACL. He will most likely miss the rest of the season. When he's done, he'll finish with 25 catches and no touchdowns this year. Brutally. Deebo Samuel also missed most of the game due to illness. Jauan Jennings was also sidelined with a hip injury. Ricky Pearsall stepped up with three catches for 21 yards in his first career game. But Jacob Cowing was the 49ers' best wide receiver on the field. He had a nice 41-yard catch after making a stutter go. He is the most explosive player on offense. He should have played the whole season.

TIGHT ENDS: B-PLUS

George Kittle had 6 catches for 92 yards but was unable to make an impact in the red zone, where head coach Kyle Shanahan has absolutely no creativity. More about him in a moment.

Offensive line: B

They gave up just one sack and held their own against a phenomenal run defense. Jake Brendel continues to commit penalties and get thrown around. He's not a good center.

DEFENSE LINE: D

They sacked Patrick Mahomes twice, but they kept rushing past him, allowing him to go for first downs and big gains, and they absolutely failed at the run considering the Chiefs gained 184 yards on the ground had. The 49ers defensive line is soft and overpaid. After the game, Nick Bosa appeared exhausted in his postgame press conference. He sat next to the media when Ricky Pearsall spoke at the podium. Pearsall was shot less than two months ago. As Pearsall left, Bosa went to the podium and a reporter asked him what he thought of Pearsall after listening to him speak. Bosa said he wasn't paying attention. Nice, Nick.

LINEBACKER: D

They also couldn't stop the run or cover backup tight end Noah Gray, who had 66 yards. Additionally, Fred Warner couldn't pass Patrick Mahomes, who looked like he was running in slow motion when he missed Warner. Bad looks.

DEFENSE: A

They thought Patrick Mahomes had the worst pass rating of his career. Deommodore Lenoir picked him – he’s having an All-Pro season. Charvarius Ward and Renardo Green were also good. And rookie safety Malik Mustapha was the best defender on the team – he's extremely explosive and violent. The other safety, Ji'Ayir Brown, isn't nearly as good.

SPECIAL TEAMS: D

They stopped a fake punt but gave up a 55-yard punt return and missed an extra point. The 49ers were expected to fire special teams coordinator Brian Schneider tonight.

Coach: F

Nick Sorensen is the 49ers' defensive coordinator simply because they made Steve Wilks the scapegoat for the Super Bowl loss to the Chiefs. In that game, Wilks' defense gave up 19 points in regulation and 25 total points including overtime. Today, Sorensen's defense gave up 28 points in regulation to a Chiefs offense that was missing Rashee Rice, Isiah Pacheco and Juju Smith-Schuster. Which means the 49ers fired the wrong guy. Wilks should continue to be the defensive coordinator. But Sorensen isn't the main reason the 49ers lost this game – Kyle Shanahan is the main reason. He's doing a terrible job this season and was terrible today. The difference between him and Andy Reid was the biggest mismatch in the game. Shanahan has a system while Reid has creativity – a big difference. So Reid was able to get his players open against man-to-man coverage, while Shanahan was unable to do the same. Shanahan's passing game is designed for rundowns when teams are playing zone coverage and focuses primarily on stopping the run. If a team like the Chiefs can kill the 49ers' running game with their front seven, they can play man coverage, and the 49ers can't beat them because Shanahan doesn't have enough man coverage beater routes in his game plans. Unlike Reid, who has a million different screens, pick plays and scratch routes he can call to free up players who can't get into the game on their own. Shanahan is a zone coverage trader. The NFL found him out. The 49ers need to fire him. He's doing a terrible job this season and his team isn't good. It's one of the most dysfunctional teams in the NFL, and that's its fault. The 49ers were expected to hire Detroit Lions offensive coordinator Ben Johnson as their head coach at the end of the season. He's much more creative than Shanahan.