Editor’s note: The 49ers break for the bye week with a 2-8 record. This is part of a series that recaps the first 10 games with an eye to the future. In this installment, we look at the team’s biggest disappointment.

A lot of the optimism surrounding the 49ers’ season was based on the projected improvements at every level of the defense from the team’s top three picks of the 2017 draft.

Defensive lineman Solomon Thomas, the No. 3 overall pick in the draft, was expected to make a considerable leap from his three-sack rookie season.

Linebacker Reuben Foster, a first-round draft pick, was being counted on to emerge into one of the NFL’s top sideline-to-sideline playmakers, as a sure-tackler and turnover-creating machine.

And cornerback Ahkello Witherspon, a third-round selection, was expected to continue to build on his encouraging rookie season to supply the 49ers with a rising performer on the other side of veteran Richard Sherman.

The fact Thomas, Foster and Witherspoon have not made improvements over their rookie seasons rates as the 49ers’ biggest disappointment through 10 games.

Thomas has endured the most hardships, which began early in the offseason when his sister died of suicide. On the field, he has not been able to earn significant playing time as part of the 49ers’ defensive line rotation.

The plan was for Thomas to start at “Leo,” the team’s pass-rush end, then move inside to rush the passer on third downs. But during the New York Giants’ game-winning drive on Monday night, Thomas was not on the field for any of the plays when the 49ers needed to generate a pass rush.

Foster’s offseason development was impacted when he was forced to remain away from the building to deal with criminal charges of domestic violence. A judge ruled there was not enough evidence to proceed with the case. But Foster was suspended for two games at the start of the season for violations of the NFL’s policies on substances of abuse and personal conduct.

Foster has appeared in only six games. He missed the past two games with a hamstring injury. When he has been on the field, he has not produced, either. He nursed a nagging shoulder injury. Foster’s 12 missed tackles is worst on the team, according to Pro Football Focus.

Witherspoon struggled to open the season, as opposing teams isolated him while ignoring Sherman’s side of the field. He lost his starting job early in the season. He started the past four games, as the 49ers enter the bye week.

Witherspoon has been targeted 50 times, according to PFF. He has surrendered 30 catches for 339 yards with five touchdowns and no interceptions. The opposition’s passer rating against Witherspoon is 113.7.

General manager John Lynch told NBC Sports Bay Area that he expects to see more from Thomas, Foster and Witherspoon in the final six games of the season to create some momentum for 2019.

“He’s got to really start being the player we all know he can be,” Lynch said of Thomas.

As for Foster and Witherspoon, Lynch said, “I expect to see great progress from them.”