There will be plenty of new faces on the Bears' sidelines this season, but how quickly can they rebuild in Chicago?

The game of football is a livelihood for just about all involved, so it's always tough to toss out criticisms like that a team "gave up" or "wasn't trying." But something looked off for the Chicago Bears down the stretch last season, as they tumbled from a 3–3 start to a 5–11 finish, punctuated by a defense that finished 31st in points allowed.

Coach Marc Trestman and his staff took the fall for that collapse. Dubbed an offensive guru, Trestman could not solve the Jay Cutler riddle in his two seasons in the Windy City—he actually had more sustained success with Josh McCown at quarterback—and the offense suffered accordingly, averaging fewer than 20 points per game in 2014. Any fingers not pointed at Trestman were directed toward defensive coordinator Mel Tucker, who could find no answers the past two seasons.

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As a result, the 2015 Bears will look plenty different, at least on the sidelines.

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If Trestman's hire was a swing for the fences by Chicago's front office, replacing him with veteran John Fox is a 180-degree turn. Fox has 13 years of NFL head coaching experience (and 119 wins) under his belt, plus two conference championships. Perhaps even more important to the cause, the defense now belongs to Vic Fangio, widely considered among the NFL's top coordinators. Adam Gase—still on track to be a head coach himself, soon—will call the shots for the offense.

"I've never predicted records," Fox said at his introductory press conference. "If I could do that I'd be at a race track somewhere. I can just say we in the past have made pretty good jumps, so we're looking to do that. I can't predict exactly how fast and when that will happen. I just believe it will."

There's a new general manager in town, too: Ryan Pace, the league's youngest GM at 37 years old. What he accomplished this off-season should, in theory, make Fox's attempt at a quick turnaround easier. Pace traded away wide receiver Brandon Marshall to the Jets for a fifth-round draft pick. He later replaced Marshall with rookie Kevin White (No. 7 overall) and signed steady veteran Eddie Royal, who is coming off a 778-yard, seven-touchdown season with San Diego. Free-agent center Will Montgomery rounded out the significant moves on offense.

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As for that middling defense, Pace's free-agent coup de grâce came in the form of ex-Ravens pass-rusher Pernell McPhee. That addition was close to a must-have with Chicago transitioning to a 3-4 scheme under Fox and Fangio. Several remaining defensive ends will slide out to join McPhee at outside linebacker, including Jared Allen, Willie Young and Lamarr Houston. Former Cardinal Sam Acho, signed in free agency, also will help.

Up front, the Bears used a second-round pick on lineman Eddie Goldman—he joins 2014 second-rounder Ego Ferguson and 2014 third-rounder Will Sutton as key pieces there. The line was too often overrun last season, though the back seven provided minimal support.

Enter ex-Buc Mason Foster at inside linebacker. He is ticketed for a starting ILB role, with fellow newcomers Antrell Rolle, Alan Ball and Tracy Porter expected to play extended minutes in the secondary. Rolle essentially replaces Chris Conte at safety, which should be a noticeable upgrade.

How quickly can Fox pull the Bears back together? He may need longer than Bears fans are hoping, especially in what has a chance to be the NFL's toughest division. The franchise needed a change, though, and there at least is a light at the end of the tunnel again.

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Grade: B-plus

Best acquisition: Pernell McPhee, OLB

The Bears' defense should be tougher to deal with head-on—Goldman is a 335-pound load in the middle, Foster is a reliable tackler and Rolle averaged 92.8 tackles over five Giants seasons. Assuming opposing teams cannot just hammer Chicago between the tackles, this unit could be a handful off the edges. That hope starts with McPhee, who chalked up 7.5 sacks last season as a rotational player for Baltimore and now gets his chance to shine as a featured piece.

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"There are a couple things that stand out with him," Pace said after signing McPhee to a five-year, $39 million contract. "First of all, he's disruptive. He hits the quarterback a ton. ... I like the violence that he plays with. He's got length, gets off blocks. I think he's a well-rounded player, too. He's a productive pass rusher but also a steady, consistent run defender."

McPhee's experience in the Baltimore 3–4 scheme may have been worth his price tag alone. Allen has been positive about his move from DE to OLB, but it's a tough move for any player, let alone a 33-year-old forced to learn a new position. The same is true for Young, Shea McClellin and Houston, who's coming off a season-ending knee injury. A sleeper in the mix: David Bass, a 2013 seventh-round pick by Oakland.

All the pass-rush potential—and the Bears' chances of sealing off the corners vs. the run—relies on McPhee continue his ascension to defensive stardom. He's capable of doing so.

Biggest loss: Brandon Marshall, WR

Anytime a new regime inherits a front office, the potential is there for sweeping personnel movement. For a bit, the clues hinted at Jay Cutler's exit, but his contract made a split unworkable.

Marshall, on the other hand, carried a reasonable contract following an extension signed last off-season—he was set to make about $7.7 million in 2015, with another $16 million or so owed him over '16-'17. In fact, those numbers were fair enough for a player with Marshall's production that the Jets bumped up his 2015 payout by nearly $2 million after trading a fifth-round pick to Chicago for the 31-year-old receiver.

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Marshall's performance last season (61 catches for 721 yards and eight touchdowns) was his worst statistically since his rookie year, although an ankle injury hindered him throughout and he missed the final three weeks with broken ribs. Back in 2013, however, Marshall hauled down 100 receptions and he finished with 118 the year prior.

While White was a game-changing playmaker at West Virginia, the rookie learning curve can be steep. Marshall's presence prevented defenses from overloading on Alshon Jeffery, and vice versa. Can White pick up the slack?

"If I could stress one word for this player: he's competitive," said Pace of White. "You see it after the catch. You see it in the way he attacks the ball in the air. This is a dynamic play-maker for our offense. I can probably tell you right now, the most excited guy in the building is [offensive coordinator] Adam Gase upstairs. ... This is a big-play weapon for us; a competitive tough player. We couldn't be more thrilled to have him."

If White is as impressive as the Bears believe he can be, Marshall's loss may be but a blip on the off-season radar. But if the passing game fails to get off the ground, expect some second guessing.

Underrated draft pick: Adrian Amos, S, Penn State

When pundits criticized the 2015 draft class for being shy of safety depth, they seemed to overlook guys like Amos—mid-to-late-round options with versatility and experience.

Chicago scooped up Amos in Round 5 and it may not take him long to solidify himself as a value. A 37-game starter at Penn State, Amos was a cornerback through 2012 before beginning his move to safety. He played well in both spots, so the Bears could use him as a backup across the board. In the immediate future Amos offers depth behind projected safety starters Rolle and Ryan Mundy.

This is one of those players who makes it easier to round out a roster because of how many different roles he can fill. Amos may be a special-teams contributor out of the gate, but he has a bright future.

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Looming question for training camp: How much difference can Vic Fangio make?

SI's Doug Farrar tabbed the Bears' move for Fangio as the most impactful move made by any team this off-season. "Fangio is one of the best at taking the talent available and moving all the pieces the right way," Farrar wrote. "His hybrid fronts and advanced coverage concepts will have the Bears competing for the NFC North title after an off-year."

High praise, indeed. Consider for a moment, though, the calamitous drop in defensive production Chicago endured post-Lovie Smith. The 2012 Bears, a 10-6 team, ranked third in points allowed and fifth in yards allowed; the '13 squad, under Trestman and Tucker, came in 30th in both categories. The defense slipped another notch last year—only Oakland surrendered more points.

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Asking Fangio to mold that mess into a top-10 unit, as he perennially had in San Francisco, is reaching for the moon. A moderate improvement followed by a big leap in 2016 is more realistic, frustrating as that may be at times this coming season.

Fangio does have his San Francisco track record on which to lean. The 49ers' defense ranked fifth or better in yards allowed during all four of Fangio's years there. His previous coordinator stop with the expansion Houston Texans was less of a hit, but even there Fangio coaxed a 16th-ranked defense out of that first season. The Bears' talent level lies somewhere between the initial Texans' roster and the 49ers' recent Super Bowl squad.

"Playing hard is important," Fangio said, via the Chicago Tribune. "But if you're playing hard and doing the wrong thing, either from an assignment standpoint or a technique standpoint, it doesn't matter that you're playing hard. So we want to be doing the right things from an assignment standpoint, doing it the right way from a technique standpoint and then play hard.

"And if we're talented enough, we'll be good."