2014 NFL free agency: Pats secondary, Bears D-line among most-improved units

Willie Young (left) was an underrated signing for the Bears. (David Durochik/AP)

While free-agency grades and evaluations are always given for the signing of individual players, it's good to look at how specific positional units are affected by offseason moves. Football is, after all, the ultimate team game and interdependent sport, and some teams seem to understand that better than others. Here are seven cases in which teams used free agency to make big blocks of their rosters much better.

New England's secondary

In 2013, the Patriots' underrated defense was led in part by stellar performances from cornerbacks Aqib Talib, Logan Ryan and Alfonzo Dennard. But Bill Belichick is always looking for new ways to run his defenses, and when Talib bailed for the Denver Broncos, change was afoot. The Patriots dropped the hammer on two intriguing signings -- first, the addition of former Jets and Buccaneers cornerback Darrelle Revis on a deal that guarantees Revis $12 million in 2014 and leaves the door open for a longer-term relationship. In addition, New England signed former Seahawks cornerback Brandon Browner to a three-year, $15.15 million contract with $1 million guaranteed. Browner will miss the first four games of the 2014 season due to his numerous dalliances on the wrong side of the NFL's drug policies, but when he's on the field, he presents some interesting options as a tall, physical press cornerback who also might play some safety or even nickel linebacker in Belichick's schemes.

There are no such variable outcomes with Revis -- like Talib, he'll be tasked with guarding the top receiver of every Patriots' opponent every week, and unlike Talib, he can stick and stay in short areas as well as any pass defender in the league. These two deals give the Pats optimal flexibility in a loaded secondary; with Revis as the point man, Browner beating up No. 2 guys and the Ryan/Dennard combo perhaps able to hit more reps in the slot, the Patriots secondary will be very interesting to watch from week to week in the new season.

Chicago's defensive line

The Monsters of the Midway were anything but monstrous in 2013 -- a formerly great defense when Lovie Smith was in charge fell apart due to talent attrition and injuries. Per Football Outsiders' defensive line metrics, only San Diego's fronts were more vulnerable against the run, and the Bears allowed a ghastly 5.34 yards per running back carry (the league average was 4.10 yards allowed). The Bears were happy to let Julius Peppers and his oversized contract go to Green Bay, and general manager Phil Emery redefined his line with authority.

Giving former Raiders lineman Lamarr Houston a five-year, $35 million deal was a brilliant move -- Houston played everywhere from three-tech to outside linebacker in Oakland's defense, and he made his bones as one of the league's most versatile players with six sacks, 16 quarterback hits, 41 quarterback hurries and 54 total stops. In addition, Emery picked off a good player from a division rival when he signed former Detroit end Willie Young to a three-year, $9 million deal. Young amassed three sacks, eight hits and 48 hurries, not to mention 31 total stops. Of course, the piece de resistance was the signing of Jared Allen to a four-year, $32 million deal with $15.5 million guaranteed, giving the Bears a major (if aging) force as a pure edge rusher. It will be captivating to see how defensive coordinator Mel Tucker moves all those pieces around, but few teams did more to shore up an overwhelming need.

New York Giants secondary

It's not that the Giants secondary was bad in 2013 -- Trumaine McBride allowed a 57.4 opposing quarterback rating, and Prince Amukamara had his high points. But in terms of depth and breadth, it's hard not to like what the G-Men did to improve their pass defense overall. They signed former Chiefs safety Quintin Demps, and added ex-Broncos cornerback Dominique Rodgers-Cromartie and cornerback Walter Thurmond, formerly of the Seahawks. Though Demps will likely make more of an impact as a return man, DRC will take his estimable coverage abilities and become an outstanding bookend for Amukamara. They re-signed McBride, and adding Thurmond in slot packages will help a great deal.

Tampa Bay's defensive line

There's little question that the Bucs won the 2014 free-agency derby, and they did so on both sides of the line. On defense, you can start with the addition of head coach Lovie Smith -- few coaches in the league better understand how to mix scheme and personnel. Despite the little disasters brought about by Greg Schiano and his assistants in 2013, Tampa Bay's defense was pretty good, and it's going to be even better with the additions of end Michael Johnson (formerly of the Bengals) and tackle Clinton McDonald (formerly of the Seahawks). Johnson was hit-and-miss as a sack artist last season, but he was a constant terror as a hurrier of opposing quarterbacks, and he's stellar against the run. Look for Smith to move Johnson inside on certain downs as he did with Julius Peppers in Chicago. And McDonald was a rock in Pete Carroll's rotation last season, providing everything from run-stopping to short pass coverage to quarterback pressures.

Denver's secondary

In Super Bowl XLVIII, the Broncos' record-setting offense was completely and totally upended by a Seahawks defense that featured aggressive cornerbacks and safeties who brought the pain on every short and intermediate route. And in free agency, the Broncos went about reversing course in a very pointed fashion. They signed Aqib Talib to a six-year, $57 million deal which is, like most NFL deals these days, a much bigger number in theory than in practice. Basically, Denver rented an aggressive press cornerback for one year and up to $12 million, depending on per-game bonuses, but it will be a serious upgrade over the unfortunate coverage Champ Bailey was handing out over the last two seasons. And in one of the better signings in this free agency period, the Broncos gave former Browns safety T.J. Ward a four-year, $23 million deal with $14 million guaranteed. Talib isn't Revis or Richard Sherman, but he's closer than anything the Broncos had last year, especially after Chris Harris was hurt. And Ward is a mid-field enforcer who gives Denver's secondary more punch than it's had since John Lynch's salad days.

Tampa Bay's offensive line

It's tough to upgrade one position any more than the Bucs did at left tackle. To replace Donald Penn and his 12 sacks, six hurries and 28 quarterback hits allowed, Tampa Bay stole Anthony Collins from the Bengals with a five-year, $30 million deal with $15 million guaranteed. Collins allowed no sacks, one hit and 13 hurries in 673 offensive snaps last season, and he's got the size and athleticism to hold the point at that crucial position for a while. The Bucs also added ex-Packers center Evan Dietrich-Smith, who ranked eighth overall at his position in Pro Football Focus' blocking metrics. Jeremy Zuttah, Tampa Bay's center in 2013, ranked 22nd. Dietrich-Smith gave up five sacks last season, but just two after Week 3. One thing's for sure -- you'll see a lot of new looks from the Bucs in their line play -- in just about every way.

New Orleans' secondary

Kenny Vaccaro, New Orleans' first-round pick in 2013, proved his value with his supreme versatility, playing everywhere from both safety positions to slot corner to linebacker depth to a guided missile in certain blitz packages. But the Saints still needed a center fielder at safety, and they got the very best one available -- and the best in the NFL outside of Seattle's Earl Thomas -- when they signed former Buffalo Bills safety Jairus Byrd to a six-year, $54 million contract with $24 million guaranteed. With Vaccaro ranging all over the place and Byrd dealing with everything between the seams ... well, it's little wonder that Saints defensive coordinator Rob Ryan is quite excited.

Ryan said of Byrd at a recent coaches' clinic

. "I was just overwhelmed, so excited about it. They [the Saints' front office] were smart about it. They know players and they know who we need and went out and got the guy we really need and I’m just so excited about it. To get this young man, it’s so awesome for us.”