We are continuing an eight-part series ranking the Oakland Raiders' position groups:

Group: Linebackers.

Ranking out of eight positions: 2; 3, quarterbacks ;4, offensive line; 5, defensive line; 6, running backs; 7, tight ends; 8, secondary.

Why: The Raiders added a starter in middle linebacker Curtis Lofton and got depth in free agency and in the draft.

Bright spots: It starts with Khalil Mack. The No. 5 overall draft pick in 2014 showed he was a complete player last season and many scouts expect him to soon become one of the game’s best defensive players.

Concerns: Sio Moore’s health. He is recovering from hip surgery. He did some work in minicamp and the Raiders hope he is ready for training camp. If Moore has no setbacks, he should start.

Outlook for 2015: This unit should be much better than the mess of a linebacker group last year, especially with its depth. It should make the entire defense better. Mack should make a bigger impact, especially in the pass-rush game. Lofton is a proven veteran and he should be better than Miles Burris was last year. Free-agent pickup Malcolm Smith and Ray-Ray Armstrong give Oakland depth and versatility on the outside. This should be one of the Raiders’ very best units in 2015.