Williams was elevated from the Cardinals' practice squad to the active roster Tuesday.
With Chris Johnson (fractured tibia) placed on IR/designated to return, Williams will join Andre Ellington (turf toe), David Johnson and Stepfan Taylor in the Arizona backfield. Interestingly enough, Cardinals quarterback Carson Palmer mentioned Williams and David Johnson, but not Taylor, when discussing the fallout from Sunday's injuries. If Ellington can't suit up, which seems likely, it's entirely possible Williams will serve as Johnson's top backup against the Rams. Williams had 53 carries for 246 yards (4.6 YPC) and two catches for 11 yards in five games with the Cardinals last season. He didn't score any touchdowns but did reach 15 carries in three separate games.