What’s wrong with Chargers’ Justin Herbert? Mike Williams, Keenan Allen might answer

Justin Herbert’s completion total and percentage are both up while he has thrown for 115 fewer yards and five fewer touchdowns.

His rating is seven points lower, and he has passed for nearly a full yard less per attempt.

Through nine games this year and nine a season ago — a season that ended with Herbert in the Pro Bowl — one thing is identical: The Chargers are 5-4.

The above math and the missing images of Herbert spiraling rainbows deep downfield have left some observers outside the team’s Costa Mesa training facility wondering why the quarterback has regressed in his third season.

“I think it has been more challenging with all of the different pieces,” offensive coordinator Joe Lombardi said. “I think when you get in a situation like that, you can push too hard and turn the ball over. For the most part, he has protected it well.

“I think, maybe, some of the opportunities to make the big plays just haven’t been there for him and he’s just trying to play smart. I’m not worried about his regression.”

For the record, Herbert had seven interceptions at this point in 2021 and six right now. He has lost one more fumble than a year ago.

There is no denying that injuries have impacted Herbert and the Chargers’ offense this season, those “different pieces” mounting by the game. Most notably:

• Keenan Allen has played only 45 snaps, half coming at perhaps three-quarter speed as he attempted to push through a sore hamstring in Week 7.

• Mike Williams has missed the last two games and has three touchdowns for the season. He had twice that many through nine games last year.

• Left tackle Rashawn Slater has been out since Week 3 because of a biceps injury while right tackle Trey Pipkins III has been in and out of the lineup while dealing with a knee sprain.

• Herbert was hurt in Kansas City in Week 2 when he suffered fractured rib cartilage, an injury that clearly limited his effectiveness until just recently.

Now comes the Chargers’ rematch against the Chiefs, Sunday night at SoFi Stadium, a Herbert-versus-Patrick-Mahomes renewal enticing enough that the NFL and NBC flexed the showdown to primetime.

Allen and Williams have been limited in practice the last two days, their availability for Sunday still in question. Both have said they want and hope to play.

“If they are going, it’s huge,” Lombardi said. “They are our two best receivers. If they are out there and healthy, it’s a big boost.”

Herbert made the first start of his career against Kansas City in 2020, throwing for 311 yards and nearly leading the Chargers to an upset victory.

Chiefs quarterback Patrick Mahomes runs for a first down against the Chargers at SoFi Stadium in 2021.

(Marcio Jose Sanchez / Associated Press)

After taking over as the Chiefs’ starting quarterback in 2018, Mahomes made his first start against the Chargers, throwing for four touchdowns.

The two players are as familiar with one another as the teams are — and nearly as difficult to separate.

Six of the last seven meetings between the Chargers and Chiefs have been decided by one score, not counting the regular-season finale at the end of the 2020 season when Kansas City already had clinched its playoff position and didn’t play its regulars.

Herbert and the Chargers are trying to bounce back from a scoreless second half Sunday night against San Francisco, the performance featuring only three first downs and 52 total yards on five possessions after halftime.

Able to convert just one of five third downs, the Chargers failed to sustain anything as they blew what once was a 10-point lead and lost 22-16.

Herbert and the offense will have to be much better against Kansas City, which leads the NFL in points per game.

“It has been a tough stretch for us, five or six games, because there has just been no continuity whatsoever,” coach Brandon Staley said. “What I am proud of is our coaching staff and our players hanging tough, and that’s what you have to do sometimes in the NFL.”

Hanging tough for Herbert on Sunday would be easier with Allen and Williams, two pieces with which he is quite familiar.

Etc.

Pipkins, wide receiver DeAndre Carter (ribs), tight end Gerald Everett (groin) and edge rusher Chris Rumph II (knee) also all were limited in practice Thursday. … Punter JK Scott (illness) missed his second consecutive day. Chargers kicker Cameron Dicker also has punted in college and during NFL preseason games.