Plenty of reasons to explain S. F.’ s disappointing record

Trent Williams: The seventime Pro Bowl tackle hasn’t been perfect, but it’s a testament to his excellence that there was much perplexed handwringing when he had a few passblocking whiffs in losses to the Eagles and Dolphins.

A side note: It’s also a reflection of the 49ers’ injury situation that other candidates for this distinction — Kittle and running back Raheem Mostert — have been too banged up to qualify.

Williams’ season has been sandwiched by moments that strongly suggest he will be a priority for the cashstrapped 49ers to resign in the offseason.

In Week 1, the 320pounder resembled a sprinter before unloading on poor Jordan Hicks — sending the unsuspecting Cardinals linebacker into Livermore — on a devastating run block that went viral. Williams is on a streak in which he hasn’t allowed a quarterback pressure, let alone a sack, in his past 115 passblocking snaps dating to Week 5, according to Pro Football Focus.

Williams’ value was highlighted Thursday night, which was the only game he’s missed. His replacement, Justin Skule, allowed a sack and pressure that led to two turnovers that Green Bay turned into 10 points.

Garoppolo: In fairness, Garoppolo made five of his six mostly uninspiring starts on a bum ankle before he made an overdue trip to injured reserve Thursday. Still, in his only healthy start, the seasonopening loss to Arizona, he missed mustmake throws on the final drive to cap a shaky performance.

And his injury history is a relevant issue: Dating to 2016 with the Patriots, Garoppolo has suffered three significant injuries ( shoulder, knee, ankle), which is a massive medical file for a player who has made the equivalent of two full seasons of starts ( 32) in his career.

There were already questions about the 49ers’ longterm commitment to Garoppolo before the season: Teams that know they have their franchise quarterback — and consistently talk about building a sustainable winner — don’t consider replacing him with a 43yearold QB, even if the old guy is the cyborg known as Tom Brady.

The 49ers stuck with Garoppolo because they believed he would take a big step in a second full season with Shanahan. His ankle injury guarantees that won’t happen. That means what happens in the upcoming offseason between the 49ers and their QB will be the question hanging over the franchise.

Fred Warner: A notable retired QB said it: “That’s the best linebacker in ball right there,” commented CBS’ Tony Romo during the 49ers’ Week 7 win at New England.

And a notable current QB has voiced the same sentiment: “You’re the best. And everybody knows it. The field don’t lie,” Green Bay’s Aaron Rodgers told the mikedup Warner after the 49ers’ loss on Thursday night.

Yes, what would have sounded wildly premature two months ago now appears obvious: Warner, 23, in the middle of his third season, is ready to assume a spot with Patrick Willis and NaVorro Bowman as one of the franchise’s great modernday inside linebackers.

The 49ers have been without most of their best defensive players for most of the season, but they’re still ranked seventh in total defense because Warner has been a middleofthefield anchoring force.

He already has a career high in interceptions ( two) and he’s on pace for a careerbest 122 tackles in a season that could finish with his first AllPro and Pro Bowl recognition.

Arik Armstead: The best thing about signing a fiveyear, $ 85 million contract is sort of obvious.

The downside: The big bank account allows for few excuses when, as a defensive lineman, you have 22 tackles and 1.5 sacks in nine games.

One reason for Armstead’s puny totals is that the absence of Bosa and Ford have forced him to line up more outside a season after he did most of damage along the interior in last year’s 10sack season. In addition, the lack of those Pro Bowl pass rushers has meant more attention on Armstead from opponents.

Still, Armstead’s payday suggested the former firstround pick had reached a level where he could overcome such obstacles. Instead, he has become invisible for long stretches: On Thursday, he did not have a tackle — and did not appear on the stat sheet — in the loss to Green Bay.

Resigning Jason Verrett: This decision seemed curious — to the few who noticed — when the 49ers brought back the former firstround pick with a list of injuries longer than a CVS receipt.

But the damagedgoods cornerback has brought the goods since injuries forced him into the starting lineup in Week 3.

Verrett has allowed just 24.9 passing yards a game in his seven starts, and QBs have a 75.6 passer rating when targeting him. In other words, he’s performed like a Pro Bowl player while earning a $ 910,000 base salary.

If he can remain healthy, he’s due for a massive raise in 2021. And it could come from the 49ers, who could decide he’s a better option to retain than Sherman, who will turn 33 in March and hasn’t played since Week 1 because of ongoing lower leg issues.

Trading DeForest Buckner: The 49ers used the money required to sign Buckner, a standout defensive tackle, to keep Armstead and free safety Jimmie Ward on longterm deals. Then they traded Buckner to the Colts for a firstround pick they used to select his far cheaper replacement, Javon Kinlaw.

However, Armstead ( see above) hasn’t built on his breakout season, and Kinlaw has work to do to become DeForest Part Deux: The No. 14 pick has 19 tackles, one quarterback hit and no sacks in nine games. ( For those curious: Buckner has 29 tackles, 13 QB hits and 2.5 sacks in seven games.)

Yes, it’s not fair to compare the justgettingstarted Kinlaw to Buckner, and besides, it’s folly to judge an interior defensive lineman solely on stats. Still, the 49ers bet on Armstead and Kinlaw and parted with Buckner, a sure thing as an AllPro and twotime captain who had missed one game in his first four seasons.

What choice did they have? What if they paid Buckner, traded Armstead in exchange for a lesser ( thirdround?) pick, let Ward walk in free agency and replaced him with promising 2018 thirdround pick Tarvarius Moore?

This GM stuff is easy after the fact.

Brandon Aiyuk’s 38yard touchdown run: The rookie firstround pick is known for gashose arms that belie his height ( 6foot) and give him the catch radius of Hakeem Olajuwon.

But this was about his freakish legs. In Week 4, against the Eagles, Aiyuk caught a lateral 6 yards behind the line of scrimmage, broke two tackles about 15 yards downfield and then came the whatjusthappened finish: With Marcus Epps closing in at a perfect tackling angle, Aiyuk leaped to hurdle the safety at the 8yard line, stopped levitating when he landed at the 3 and barreled into the end zone.

Frank Gore’s 4yard run: It was an innocuous upthemiddle run by the 49ers’ alltime rushing leader, now playing for the Jets, in the first quarter of the 49ers’ win in Week 2.

And it included a crippling blow to the 49ers’ vaunted defense: Lined up at right defensive end, Bosa’s left knee buckled when he was engaged with tight end Trevon Wesco.

Bosa initially stood up, went down on all fours, beckoned the sideline for assistance and was soon carted off the field. There are other reasons the 49ers rank 23rd in sacks per game and no longer scare QBs, but Bosa’s absence due to his torn ACL is, by far, the biggest.

Eric Branch covers the 49ers for The San Francisco Chronicle. Email: ebranch@ sfchronicle. com Twitter: @ Eric_ Branch