By Dan Durkin-

Editor’s note: This is the ninth and final 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.

(CBS) Just a few seasons ago, the Bears offset their deficiencies on offense by playing tough defense and winning the field position battle with stellar special teams units. Yet, in just two seasons, the latter phase has rapidly gone from a strength to a weakness.

In special team’s parlance, “core four” refers to the coverage and return units on both punts and kickoffs. For the Bears, there was a subset core four that once made those units special – coordinator Dave Toub, returner Devin Hester, kicker Robbie Gould and long snapper Patrick Mannelly. From that group, only Gould remains, and the other roles haven’t been properly addressed.

Toub was the first domino piece to fall. After he didn’t make it past the first round of interviews for the Bears’ head coaching vacancy in January 2013, he took over the special teams coordinator role with the Kansas City Chiefs and quickly turned them into one of the league’s best.

Rick Gosselin of The Dallas Morning News does an annual ranking of special teams units league-wide, and in those, Toub took the Chiefs from 23rd in 2012 to third overall in 2013 and eighth overall in 2014.

On the other hand, the Bears took a tumble, falling from ninth in 2012 to 23rd in 2013 and 26th in 2014. Former coordinator Joe DeCamillis (now the Broncos’ special teams coordinator) deserves some blame, but he wasn’t given much to work with in his tenure from a personnel perspective by former general manager Phil Emery, and DeCamillis’ coaching style didn’t mesh with that of former head coach Marc Trestman.

Compared to how much they were focused on under Lovie Smith, special teams were de-emphasized under Trestman. When the team addressed the media during last season’s bye week, Emery admitted that he was using the special teams groups as a means of trying to develop young talent on the roster.

The Bears’ plan for the 2014 season was to build an early lead with their offense to make their opponent one-dimensional so they could pin their ears back and rush the passer. That plan only came to fruition once, against the Atlanta Falcons. Special teams’ role in this plan was to provide favorable starting field position to start drives. From 2012 to 2014, the Bears dropped from fourth in average starting field position to 26th in 2014.

One of the biggest miscalculations Emery made was how he handled the returner position. The team successfully lured Chris Williams from the Saints’ practice squad with a $100,000 signing bonus three days prior to the 2013 season ending.

Williams made a splash play last preseason on a 73-yard reception, but he pulled his hamstring in the process. The injury lingered and ultimately led to him not making the final 53-man roster. The Bears started the season with Senorise Perry as their primary kick returner and Santonio Holmes as their punt returner.

The return units provided no lift in field position. In fact, they didn’t crack the 20-yard line on a kickoff return until Week 7.

In the end, the Bears cycled through Perry, Rashad Ross, went back to Williams (who was eventually waived on Dec. 6) before signing Marc Mariani to a two-year contract on Nov. 18. Mariani brought some stability to the position and is under contract in 2015, but more competition is needed at the position.

The Bears spent a sixth-round draft pick last spring on punter Pat O’Donnell, who became a cult hero in training camp. While O’Donnell did have some strong performances throughout the season, he finished with a lower net punting average than Adam Podlesh — the player he replaced — had the previous season.

It’s also worth noting that Tress Way, who was competing with O’Donnell in training camp, latched on with the Redskins and finished top in the league in gross punting average (47.5) and 10th in net average (40).

After signing a lucrative four-year extension last year with $9 million guaranteed — the highest ever by a kicker — Gould had his worst season as a pro, finishing with career lows in field goals attempted, made and percentage. Gould was hampered by a quad injury that forced him to miss the final four games of the season and was replaced by veteran Jay Feely.

The youth movement on special teams made the units look largely uncoordinated. Penalties were consistent and costly. However, it’s hard to expect positive results when the nucleus is primarily made of undrafted free agent rookies.

In years past, the Bears had veterans like Brendon Ayanbadejo, Tim Shaw, Eric Weems and Blake Costanzo who made a career off of special teams. Such players not only served as strong voices in the meeting rooms, they also showed younger players that there are alternate ways to ensure yourself a spot on a 53-man roster.

Looking ahead, the Bears’ potential switch to a 3-4 defense may boost special teams, as the team will likely carry more linebackers, which typically comprise the core coverage and return units.

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