The Detroit Lions are on pace to have the worst rushing attack in the 32-team era.
They are currently averaging 66.9 yards per game, which is the lowest mark seen since the 2000 San Diego Chargers (66.4 YPG). To put that in perspective, it would currently take the Lions two-and-a-half games to catch the 31st-ranked Cleveland Browns (on their bye this week).
The schematic issues have been covered extensively. Outside zone runs, or stretch runs, don't play to the offensive line's talents. Then again, the lack of said talents is a problem in and of itself, but that's a different discussion.