By Dan Durkin-

Editor’s note: This is the third part in a series that takes an all-encompassing look at the state of the Bears’ roster. Click here to read breakdowns of the other positions.

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(CBS) The vast majority of blame for the Bears’ defensive failures in 2014 was directed at the coaching, more specifically Mel Tucker’s coordination of the unit. Such criticism is fair.

The Bears ran a vanilla scheme that deployed static views that opposing quarterbacks were able to quickly diagnose. Wrinkles to create pre-snap confusion were sparse, as were post-snap disruptions with line games and pressure packages.

However, as we’ve covered so far in the positional breakdown series, the Bears’ back seven on defense was talent poor, which played a part in the dismissal of general manager Phil Emery.

Whether you’re talking about issues with the front seven or back seven, the linebackers are always included. When you isolate and assess the performance of the linebacking play for the Bears in 2014, it was as poor as it gets in the NFL. Injuries and youth played a part in the collective struggle, but players were also playing out of position.

Tracing all the way back to training camp, the linebacking corps was unsettled.

The Bears used a variety of combinations, but when camp broke, they settled on a base package of Lance Briggs on the weak side (Will), D.J. Williams in the middle (Mike) and Shea McClellin on the strong side (Sam). Their nickel package featured Briggs and Jon Bostic.

As the season progressed, injuries to the starters — McClellin (broken right hand), Briggs (ribs), Williams (neck) and Bostic (back) — affected continuity. By the end of the season, the Bears used nine different starting linebacker combinations, and Briggs, Williams and Darryl Sharpton (hamstring) all ended up on injured reserve.

Combined with the overall lack of experience of the replacement players, the constant rotation had a negative impact.

Linebackers have the most responsibilities on the defense. They set the front based on how the offense is lined up and are counted on to fit gaps in the run game as well as drop into coverage against the pass.

Quarterbacks manipulated the Bears’ second level on play-action plays to create voids and passing windows between the underneath and deep defenders. Linebackers also gave free releases — which falls on coaching as well — to tight ends and receivers, enabling them to quickly get into their routes unobstructed.

Football Outsiders’ Defense-Adjusted Value Over Average (DVOA) statistic ranked the Bears’ pass defense last in the league against tight ends this past season. In total, the Bears gave up 13 touchdowns to tight ends.

Of all the positions to project for the upcoming season, linebacker is the most challenging.

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Briggs, Williams and Sharpton are unrestricted free agents. The Bears have six linebackers under contract — McClellin, Bostic, Khaseem Greene, Christian Jones, DeDe Lattimore and Jonathan Brown, who was signed to a future/reserves contract. Bostic and Jones gained valuable experience in 2014, ranking first and third in tackles, respectively.

While the Bears haven’t come out directly and said that they’re moving to a 3-4 defense, the coaching hires they’ve made on the defensive side of the ball — particularly with Clint Hurtt as the outside linebackers coach — signal such a change is in the offing.

The changes are drastic. From a roster standpoint, the team will carry more linebackers. From a scouting standpoint, a different profile of athlete will be sought after. From a schematic standpoint, base packages and 2-4-5 nickel packages will deploy four linebackers, with the extra or “Jack backer” being on the inside.

For purposes of this preview, a switch to a 3-4 has been assumed, so how does the current group of players under contract fit in the potential new scheme?

Bostic primarily played middle linebacker in a 4-3/Cover-3 base defense at Florida. On the other hand, Jones played three different positions — rush linebacker, inside linebacker and five-technique defensive end — in a 3-4 front at Florida State. McClellin also played in a 3-4 at Boise State. Like Jones, McClellin was used in a variety of roles in a 3-4 in college, playing inside on base downs while moving to the edge on passing downs.

Bostic could compete for the Jack-backer role, but the Bears lack a true middle linebacker who can be a force against the run. Free agents like David Harris (Jets) and Brandon Spikes (Bills) have experience inside in a 3-4 and are strong run defenders.

In the draft, Mississippi State’s Benardrick McKinney is an elite size-to-speed prospect who could play inside in a 3-4, but spending the seventh overall selection on him could be a reach.

The real issue becomes identifying an outside linebacker who can generate a pass rush, which is arguably the Bears’ biggest need heading into the offseason.

Lamarr Houston played both inside and outside in a 3-4 in Oakland and is a player who transcends scheme. How he quickly recovers from his ACL surgery and which role the team wants him to play remains to be seen.

Keep an eye on how the Bears choose to utilize players like Cornelius Washington and David Bass. Washington played both five-technique and outside linebacker in a 3-4 at Georgia. Bass has shown the suddenness to potentially play outside in a 3-4.

Defensive end Jared Allen is set to be Chicago’s highest-paid player in 2015. He doesn’t have the size or skill set to play five-technique in a 3-4, nor does he have the experience or footwork to be consistently used in coverage. Thus, if he’s kept, he may be used in nickel sub packages on the edge.

Kansas City’s Justin Houston will be the most coveted 3-4 outside linebacker, but it’s unlikely the Chiefs will let him hit the open market.

The draft seems to be an ideal spot for the Bears to address their needs for an edge rusher. If Nebraska’s Randy Gregory were to somehow slide to the Bears, he’d be an ideal fit, but that scenario seems unlikely. The Bears may center their scouting focus around players like Florida’s Dante Fowler Jr. and Missouri’s Shane Ray.

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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.