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

DEFENSIVE BACKS 

After years of being the team's Achilles heel, the Lions' secondary could be a team strength in 2015 after some better-than-expected play last season.

Led by veterans Glover Quin, James Ihedigbo and Rashean Mathis, and with Darius Slay a potentially ascending player, the Lions' defensive backs will try to lock down some dangerous receivers in the NFC North, as the defense tries to repeat its success after ranking second overall and 13th against the pass in 2014.

Quin established himself as a top free safety last year, leading the NFL with seven interceptions. Beside him, Ihedigbo became a feared thumper as he forced three fumbles and had four interceptions in 13 games, though his late-season struggles could be cause for concern as he'll be 32 by the end of the 2015 campaign.

At cornerback, Mathis and Slay provided good balance and versatility last year. Mathis brings more than a decade of experience — again, the age could be a concern as he'll be 35 next month — and Slay has the speed and strength to go toe-to-toe with top receivers.

While the starting group is set, there will be several players battling for the remaining roster spots in the defensive backfield. The Lions signed Taylor Mays, a former second-round pick, hoping he could have a career renaissance, and Josh Wilson could provide the veteran stability the Lions have lacked in the slot.

Plus, the selections of Alex Carter in the third round and Quandre Diggs in the sixth could provide improved depth for a group that struggled with injuries in 2014.

Roster locks: Safeties — Glover Quin, James Ihedigbo, Isa Abdul-Quddus. Cornerbacks —Darius Slay, Rashean Mathis, Alex Carter (R), Quandre Diggs (R).

Bubble: Safeties — Don Carey, Taylor Mays, Nate Ness, Brian Suite (R), Isaiah Johnson (R). Cornerbacks — Josh Wilson, Nevin Lawson, Chris Owens, Mohammed Seisay, Crezdon Butler, R.J. Stanford.

Roster spots: Four or five safeties, five or six cornerbacks.

Top camp competition: The nickel cornerback competition is wide open with Wilson, Diggs and Lawson as the frontrunners. The 6-foot Carter could be involved if Lions choose they want a bigger nickel option.

Rookie outlook: Carter likely will be the top backup on the outside while Diggs competes for time in the slot, and both players should have a role on special teams with strong tackling skills.

Breakout candidate: Carter, who displayed excellent cover skills at Stanford. The 6-foot-2 Suite or the 6-foot-1 Johnson could be a developmental safety similar to Jerome Couplin last year.

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