The biggest key to the Lions backfield success is the development of Ameer Abdullah. As a rookie last season, he was plagued by ball security issues early in the campaign, but closed out the year strong. He averaged 4.7 yards per attempt and put the ball on the ground just once across the final eight games. That's a stat line that should excite. Now it boils down to a smooth recovery from offseason shoulder surgery and if he can handle an increased workload.
Theo Riddick is what he is, a below-average runner, but elite receiver out of the backfield. He's a key offensive cog after catching 80 passes last season, but expecting significant growth as a ball carrier borders on unreasonable.
There are some threats to Abdullah's workload, but this particular writer doesn't even predict one of them - Stevan Ridley - makes the roster. That would leave Zach Zenner as perhaps the main threat to take away carries. It's a situation to keep an eye on because depending who makes the roster, Abdullah's value could rise and fall greatly.