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Lions linebacker Tahir Whitehead was among a handful of players who took a big leap forward in Year 1 of the Jim Caldwell era.

(Melanie Maxwell | MLive.com)

ALLEN PARK -- The Detroit Lions have been hit pretty hard for their underwhelming start to the offseason.

That includes allowing the team's greatest defensive player in a generation, Ndamukong Suh, to skip town in the prime of what could prove to be a Hall of Fame career.

They watched Nick Fairley walk, too.

The Lions acquired Haloti Ngata in a trade, which mollified some of the concern over losing Suh, or at least delayed it for a year. They signed a promising pass-rusher in DT Tyrunn Walker.

Detroit has downgraded at the position overall, though, and has yet to make any additions -- i.e., improvements -- elsewhere on its roster. That means it has backed itself into a situation where it has to get better in the draft, or maybe not get better at all this offseason.

But there's another variable that has gone a little overlooked. And that's improving the players who are already on the roster.

And player development was a strong suit of Jim Caldwell and this staff, particularly on defense. Several players made big leaps in Year 1 of this regime, including:

LB Tahir Whitehead: Don't waste your time trying to find another player who improved more from 2013 to 2014 than this guy. It can't be done.

Whitehead didn't play a lick of defense under former coach Jim Schwartz. Not even one snap. But this staff saw something it liked early on, and gave Whitehead some meaningful practice snaps at middle linebacker during the summer.

Then they moved him into the starting lineup on the strong side in the preseason. Then gave him the starting job to open the season. And when longtime starter and team leader Stephen Tulloch went down in the middle in Week 3, Whitehead had both experience in the middle in practice, as well as game experience from the strong side.

The transition was a little bumpy early on, but Whitehead was strong down the stretch. He finished the year with 86 tackles -- trailing only tackling machine DeAndre Levy on the team -- and was rated by ProFootballFocus as the 14th-best interior linebacker in the league.

The Lions' defense finished second overall, and first against the run, despite losing a starter as important as Tulloch. And the coaches deserve a tip of the hat for Whitehead's role in all of that.

As Martin Mayhew, the guy who drafted Whitehead, put it: "I never really viewed Tahir as a MIKE 'backer. I thought of him more as an outside guy. We had discussions about that. (The coaches) felt very comfortable he could adapt to the MIKE linebacker position, and he did. He did a phenomenal job in there playing for us."

CB Darius Slay: The cornerback enlisted Rod Woodson to develop his game last season, plus worked closely with Rashean Mathis and Teryl Austin when he was around the team. And it all paid off with a jump from 92nd to 19th at the position according to PFF.

Slay deserves a lot of the credit for taking the initiative to improve away from Allen Park. But Austin's scheme was a perfect fit for Slay's athletic skill-set, and deserves credit as well for getting the best out of the up-and-coming cornerback.

DT Nick Fairley: A knee injury derailed what could have been a monster season for the defensive tackle. But even that can't undo all the good work the coaching staff (and front office) did to get this guy at his best.

Fairley was notorious for his ballooning weight and questionable work ethic under Jim Schwartz. But Caldwell pushed all the right buttons in the offseason, notably benching him during training camp -- something Schwartz never did, no matter how big Fairley got.

Caldwell showed guts with that move. And it proved to be the wake-up call Fairley needed. He hired a personal chef, dropped more than 20 pounds and was a defensive force unlike ever before until a season-ending injury in Week 8.

S Glover Quin: The veteran safety was already a good player when this staff arrived, so Quin's big season might have been more about the scheme than actual skill development. But a part of developing players is understanding what they can and can't do well, and fitting them in accordingly. And this staff certainly did that at safety.

Recognizing Quin was at his best in coverage, Detroit signed James Ihedigbo to do the heavy hitting in the box. That freed up Quin to patrol the back ranks full time, and he did it as well as almost anyone in the league. He picked off an NFL-best seven passes, and made his first Pro Bowl and All-Pro teams.

WR Corey Fuller: By now you've surely recognized a trend. Like, all the Lions' most improved players were on the defense. (And that makes sense, given that the defense rocketed from 16th to second, while the offense plummeted from sixth to 19th.)

But Fuller was another nice success story of player development. The former quarterback played only one year of receiver at Virginia Tech, and was among the Lions' rawest players during his rookie season in 2013.

But he was among its most improved players in 2014, eventually winning a roster spot over Kris Durham -- the No. 2 receiver from the previous season -- and then a playing role over Ryan Broyles -- a former second-round draft pick.

He didn't do a whole lot in the regular season, finishing with 14 catches for 212 yards and one touchdown. But he did catch a game-winner against New Orleans, which helped springboard Detroit to that run of three straight comeback wins, and four straight wins overall.

So, yeah, it's fair to be concerned the Lions haven't done much about upgrading their roster this offseason. There are holes all over the place, and they'll be on the clock only three times in the first 200 or so draft picks after trading away their fourth- and fifth-round selections in the Ngata trade.

But it's important to remember that improvement can also be achieved from within. And there was a lot to like on that front during Caldwell's first season, particularly on defense. A lot of players got a lot better.

Continuing that arc on defense, while catching up on offense, would go a long way toward helping to offset some of the losses that have occurred this offseason.

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