https://www.profootballfocus.com/news/pro-nfl-run-defense-rankings-all-32-teams-entering-2018
28. SAN FRANCISCO 49ERSTOP THREE RUN-DEFENSE GRADES AMONG RETURNING PLAYERS:
Reuben Foster, linebacker – 90.9 run-defense grade
DeForest Buckner, defensive interior – 82.6
Arik Armstead, edge defender – 79.7
Missed tackle % on run plays, 2017: 11.4% (16th)
The 49ers run defense rank suffers here from the lack of a true nose tackle. 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.
I really hope DJ Jones steps up or Sheldon Day beats out Mitchell at NT. Earl Mitchell has no business starting. He is a good veteran to have around because of his work ethic and hustle but he is a liability.