Relegated to the bench in favor of Tre Mason last October, Stacy managed just 293 yards on the season after rushing for 973 yards in an impressive rookie campaign.
Similar in skill set as a downhill chain-mover, Stacy will provide insurance in case Ridley suffers a setback in his return from ACL surgery.
The Rams selected Baylor linebacker Bryce Hager with the seventh-round pick acquired in the Stacy deal.
The latest Around The NFL Podcast breaks down the 2015 NFL Draft, picking out the biggest winners and losers. Find more Around The NFL content on NFL NOW.