Upon his signing last year, San Francisco 49ers defensive tackle Earl Mitchell was seen as someone who could help a struggling run defense which ranked last in the NFL the previous season. In fact, no team in franchise history had given up more rushing yards than the 2016 squad.

Pro Football Focus continues its 32-team offseason rankings with the run defense being the latest entry in the series. The analytics site ranks the 49ers' unit at No. 28 while noting that the team needs a true nose tackle to improve.

"The 49ers run defense rank suffers here from the lack of a true nose tackle," writes Pro Football Focus. "Earl Mitchell's 5.0 run-stop percentage was the worst of any player in the NFL last season that had at least 300 snaps against the run."

Below are the top three 49ers when it comes to run-defense grades.

  1. Reuben Foster, LB, 90.9 run-defense grade
  2. DeForest Buckner, DT, 82.6
  3. Arik Armstead, DE, 79.7

The Pro Football Focus analysis team notes that the 49ers missed 11.4 percent of their tackles on run plays, which ranks at No. 16 in the NFL.

The 49ers run defense did see an improvement last year over the previous season. The unit allowed 165.9 rushing yards per game in 2016. That number improved to 116.3 in 2017, which ranked 22nd in the NFL.

Former NFL center turned NFL Network analyst Shaun O'Hara noted on Good Morning Football on Thursday that the team used three first-round selections on defensive lineman (Arik Armstead, DeForest Buckner, Solomon Thomas) from 2015 through 2017 and used another on linebacker Reuben Foster. That is a substantial investment in the 49ers' defensive front.

"Yet, the 49ers defense ranked dead last against the run over the last two years," O'Hara said.

The 49ers' ranking by Pro Football Focus was the worst among NFC West teams with the Los Angeles Rams coming in at No. 21, the Arizona Cardinals at No. 23, and the Seattle Seahawks at No. 24.