Lions training camp position previews: Running backs

This is the fifth in a series of position previews ahead of the start of Lions training camp on Monday.

RUNNING BACKS

The Lions ranked 28th in rushing in 2014, and even though a hampered offensive line played a role, they're hoping for a better performance from the backfield in 2015.

With Reggie Bush gone, Joique Bell becomes the de facto starter, a role he essentially held for most of 2014 as Bush struggled with injuries and inconsistent play.

However, Bell will start training camp on the physically unable to perform list, and even though he's supposed to recover from his knee and Achilles tendon injuries for the season, his absence will give younger players a chance to steal some of his touches.

Theo Riddick proved to be a reliable receiving threat last year with good hands and better run-after-catch skills. However, Riddick has yet to establish himself as a runner, averaging 2.6 yards on his 29 carries the last two seasons.

Bell, meanwhile, averaged 3.9 yards per carry the last two seasons, and despite a strong finish to 2014, his mediocre speed could give second-round pick Ameer Abdullah a chance to become a key cog in the offense as a rookie.

During summer workouts, Abdullah appeared to have better hands and instincts than Bush, and if the Lions choose to split touches like they did the past two years, Abdullah could quickly command a large role, especially after showing solid receiving skills.

The Lions lost fullback Jed Collins this offseason, but fifth-round pick Michael Burton should step into that role immediately.

Roster locks: Joique Bell, Theo Riddick, Ameer Abdullah (R), FB Michael Burton (R)

Bubble: George Winn, Zach Zenner (R), Desmond Martin (R), FB Emil Igwenagu.

Roster spots: Five, including fullback.

Top camp competition: With Bell still recovering from injury, Riddick and Abdullah will have a chance to fight for a bigger role at the start of the season.

Rookie outlook: Abdullah will likely open the season as the return man and should have an increasing role on offense throughout the season. Zenner and Martin must excel on special teams to earn Winn's job, but could be practice squad candidates.

Breakout candidate: Abdullah. He could be the primary ball carrier by midseason and can run inside despite being 5-foot-9.