San Francisco 49ers

Where have you gone, 49ers’ defensive-line depth?

DeForest Buckner (99) and the 49ers defensive line run drills during practice at Levi’s Stadium on June 13 in Santa Clara.
DeForest Buckner (99) and the 49ers defensive line run drills during practice at Levi’s Stadium on June 13 in Santa Clara.

When Solomon Thomas became the third consecutive defensive linemen the 49ers drafted with their top pick, fans shrugged and said, “At least the D-line will be loaded and the team will be able to rotate heavily at the position.”

Well, not so fast.

San Francisco heads into Sunday’s game against the Arizona Cardinals with one of those first-round picks, DeForest Buckner, playing more snaps through three games than he did at this point last year, with no one on the depth chart behind Thomas and with just three sacks this season. Only the Tampa Bay Buccaneers have fewer, and they’ve played just two games due to Hurricane Irma.

Where did that defensive-line depth go?

▪ Tank Carradine, a former second-round pick, is on injured reserve with a high-ankle sprain. He must miss at least eight weeks, meaning the earliest he can return is the Nov. 26 game against the Seattle Seahawks. With Carradine out, Thomas is expected to start at the so-called “big end” spot.

▪ Ronald Blair began the season on injured reserve with a thumb injury. He plays the same position as Thomas and Carradine. He can’t return until Nov. 5 against Arizona.

▪ Earlier this month, the 49ers released Quinton Dial, who started 26 games in the last two years. He played 18 snaps Sunday for his new team, the Green Bay Packers. Teammate Ahmad Brooks, who was cut by the 49ers in August, played 32 snaps.

▪ The 49ers placed Chris Jones, who had been Buckner’s backup in training camp, on injured reserve with a groin injury before setting the 53-man roster. That means he cannot play this season. They signed former Cleveland Browns lineman Xavier Cooper to be Buckner’s backup, but he’s been inactive for two of the three games.

The result is that the 49ers haven’t had the wave-after-wave rotation they envisioned heading into the season.

In the spring, defensive coordinator Robert Saleh and defensive line coach Jeff Zgonina heavily criticized Buckner’s hefty snap count – 1,005 on defense alone, the highest of any defensive tackle in 2016.

“I don’t like to see a guy play over a thousand snaps in a season like he did last year,” Zgonina said. “Especially with a rookie – that’s a lot of snaps.”

Said Saleh: “When you look at a guy like Buckner last year having played (over) 1,000 snaps – in my mind, that’s criminal. Ideally, all of them are working about 500, 600 snaps and trying to utilize everything they’ve got every snap that they’re on the football field.”

Buckner has played 179 defensive snaps so far, the most of any defensive tackle in the NFL. At that pace, he’d finish the season with 955 snaps. (Arik Armstead isn’t far behind with 172 this season.)

Saleh and Zgonina are finding out what last year’s coaches learned about Buckner: He doesn’t like to leave the game; has the stamina to play at a high level despite a huge snap count; and like last year the drop-off in talent is sharp when Buckner’s not in the game.

Saleh began softening his stance on Buckner’s 2016 play time as the season drew closer.

“I don’t want to put a number on it,” he said when asked Aug. 29 about Buckner’s ideal snap count. “We have a vision of what we’d like to see, but sometimes you get into a pickle. So with DeForest, there were so many injuries a year ago that they were probably stuck playing him. So it just wasn’t an ideal situation for the year, especially with all the injuries they suffered.”

Buckner’s and Armstead’s playing time likely will tail off a bit in coming weeks.

The 49ers have faced three running offenses, which meant a lot of snaps for base defense players like Buckner and Armstead, not so much for the team’s pass rushers. Defensive ends Aaron Lynch and Elvis Dumervil, for example, played 24 snaps combined last week against the Rams, who rarely put themselves in third-and-long situations.

Cooper, meanwhile, likely will be in uniform Sunday because the 49ers need another body with Carradine out and because coaches like Cooper’s pass-rush skills. Arizona, which lost starting running back David Johnson to a wrist injury in Week 1, has attempted 132 passes so far, second in the NFL. Cooper could boost the pass rush and provide Buckner with some rest.

Matt Barrows: @mattbarrows, read more about the team at