I would have been with you a month ago, but the run D has been much improved since the bye, shutting down Sanders, Hyde, and McCoy and limiting Elliott to a pretty pedestrian day. Even yesterday, the run D was horrible on the opening drive (8 carries for 68 yards) but allowed 96 yards on 24 carries the whole rest of the game (a mediocre 4.0 YPC). Cincinnati's two longest runs of the day were on their first drive.
Am I cherry-picking? Sure, but over the whole season, the run D is down to 4.3 YPC against (exactly the league average), which ranks 17th, almost dead middle of the pack.