By Dan Durkin—

Editor’s note: This is the third piece in a series previewing the 2015 Bears as the first training camp practice approaches July 30. You can find them in one spot here as they’re posted.

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(CBS) After taking time to look under the hood at what made Bears defensive coordinator Vic Fangio’s defense so successful over the past four seasons in San Francisco, it became readily apparent that the inside linebackers were the engine of the defense. They were coordinators on the field who set the front, then were kept clean to read, react and be downhill enforcers against the run or relied upon as underneath zone and matchup pass defenders.

In Chicago, Fangio doesn’t have talents like Patrick Willis or NaVorro Bowman to work with. Rather, he’ll be working with the youngest position group on the Bears’ roster, none of whom have NFL experience in a 3-4 defense.

Last season, Bears linebackers endured a rash of injuries that forced nine different starting combinations onto the field. Such turnover led to inconsistent play, but it did afford valuable playing time for still-developing prospects.

This season, the competition will center around four players for two positions.

Likely starters:
Mike linebacker: Mason Foster (26, fifth year),
Jack linebacker: Christian Jones (24, second year)

Other competitors: Shea McClellin (25, fourth year), Jon Bostic (24, third year), DeDe Lattimore (24, second year), Jonathan Brown (23, first year), Jonathan Anderson (23, rookie) and John Timu (22, rookie)

Key contributor: Mason Foster

Entering just his fifth season, Foster already has 54 NFL starts under his belt. He’s commanded a huddle and set fronts since 2012. Orchestrating pre-snap alignments for 10 teammates, then processing your own pre- and post-snap keys are demanding-yet-valuable tasks for a young linebacker and an asset for Foster heading into camp.

In four NFL seasons in Tampa Bay, Foster went through a position change and three different schemes. He was a weak-side linebacker in college (Washington) who transitioned to the middle for the Bucs. Schematically, he went from Raheem Morris to Greg Schiano and most recently Lovie Smith.

Foster struggled to adapt to playing the Mike linebacker role in Smith’s Tampa-2 scheme last season. Frankly, it was a role for which he was miscast. His forte is reading and reacting downhill against the run, not turning his hips to carry receivers up the vertical seam and effectively becoming a third safety in a Tampa-2 shell. A dislocated shoulder caused him to miss six games, and his productivity took a dip.

Foster will be learning yet another new system under Fangio, but his skills, physicality and instincts are well-suited for an inside linebacker role in a 3-4.

Foster’s still an ascending player. Given his experience and age, surely he didn’t anticipate his second NFL contract — typically the most lucrative for players who came into the league under the current CBA — to be a one-year, minimum value, “prove-it” deal, yet that’s exactly what he’ll play under this season. Such deals serve as motivating factors for players, and Foster has a chance to parlay this season into longer-term security.

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Potential breakout player: Christian Jones

When he came out of Florida State in 2014, I had Jones as the second-highest graded inside linebacker — trailing only Alabama’s C.J. Mosley — and a solid second-round prospect. However, character concerns and a failed drug test at the combine greased his slide right out of the draft. Every year, undrafted rookies play significant snaps, as Jones did last season.

Jones is highly athletic and possesses unteachable bend and flexibility for a man his size. There are several teachable moments from his rookie tape. However, there were also flash plays that show he physically belongs at the NFL level. It’s now just a matter of finding the right spot for him, so that his instincts and athleticism can take over.

Finding a position for Jones has been a challenge for coaches since college. He played middle, weak- and strong-side linebacker as well as rush end in both 3-4 and 4-3 schemes for the Seminoles.

As is the case with most linebackers, Jones is better playing toward the line of scrimmage rather than backing away from it, but he did show some fluidity in pass coverage last season. He needs more film study to recognize formation and alignment alerts, which will help slow the game slow down for him.

Of all the young defensive prospects on the roster, Jones has the highest athletic upside. With a strong preseason performance, he has a chance to earn a spot for years to come.

Final thoughts: This will be a compelling competition to monitor throughout the preseason. Foster, Bostic, McClellin and Jones are all promising young athletes, but can they become three-down, playmaking generals on the field that Fangio’s scheme requires?

The fact that the previous regime spent early selections on McClellin and Bostic is moot. This is a new staff and personnel department with no loyalties to the past. So playing time will be earned, not force fed.

With Foster and McClellin on one-year deals, both of are auditioning for not just the Bears but 31 other teams. Thus, they are literally incentivized to perform.

Bostic hasn’t been healthy enough to participate in offseason drills due to a lingering back injury. But his versatility was on display last season, playing all three linebacker spots and finishing second on the team in tackles.

Jones is the wild card of the bunch. He’s clearly the best athlete with the highest upside but is the least experienced. Can he pick up the scheme well enough to let his instincts take over during games?

Some of the major concerns for the group are pass coverage (an area none of them stand out in), commanding a huddle and playing the pre-snap chess match with opposing quarterbacks to keep the defense apprised of their proper alignment and assignment.

Position grade: C.

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Dan Durkin covers the Bears for CBSChicago.com and is a frequent contributor to 670 The Score. Follow him on Twitter at @djdurkin.