He'll be the backup there. They have a STUD RB in Oakland named Latavius Murray who's basically a younger, faster version of DeMarco Murray who can pass pro. His prototype is actually closer to AP and after the Rams shellacked the Raiders 52-0, the Raiders started Murray and he went off and led them to a 24-13 upset victory over the 49ers where Derek Carr threw 3TDs.
When we got Zac Stacy in the 5th in 2013, I banged the table for this guy and the Raiders got him in the sixth out of UCF.
Trent Richardson is just depth. Latavius Murray is legit and running behind their improved OL will only yield improved results.