Most people would say Zach Mettenberger here. That is a valid answer, but I am going to take it a different direction. What a rookie quarterback needs to find success is a good solid running game.
Bishop Sankey needs to step up and be this team's MVP in the second half of the season. He was the first running back taken in the draft. The Titans liked him so much because they believed he was a complete back and could step right in.
Sankey hasn't been bad, but he also hasn't made that much of an impact to this point. That is not all his fault by any means. Ken Whisenhunt does a terrible job with the running back rotation. Leon Washington should never get a carry or catch a pass. Those snaps should go to Sankey every time.
With all of that being said, Sankey still needs to make a big play. He needs to break off a big run that changes a game for this team. That will have defenses fearing the run and open up things for Mettenberger all over the field.