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Seahawks, 49ers lead the list of NFL's top defenses

Pete Carroll and Richard Sherman may hold the key to the NFL's best defense in 2013. (McClatchy-Tribune via Getty Images) Pete Carroll and Richard Sherman hold the key to what may be the NFL's best defense in 2013. (McClatchy-Tribune via Getty Images)

A generation ago, NFL defense was about aggressive coverage, beating your man at the line, and relatively simple "if this/then that" pattern-read concepts. As much as the league's great defenses are always about talent, they're more about scheme than ever before these days. In the truly modern NFL, defenses substitute entire positional rotations, play nickel and dime defense at least half the time, and must counter offenses looking to stretch the field in ways we've never seen. Add a dizzying array of option routes, more and more option quarterbacks who can actually throw the ball, and a new emphasis on speed no-huddle sets, and it's clear that the task of providing premium NFL defense on a week-to-week basis (never mind season-to-season) is tougher than it has ever been before.

Thus, the onus is on general managers, head coaches, and defensive coordinators to not only find the best players, but to specify and scout those players who are best for their systems. More defensive players are specialists these days -- nickel corners, rush ends, linemen for heavy packages, and half-field defenders masquerading as linebackers.

NFL teams capable of putting great defenses on the field should be credited more than ever for doing so, because it's a post-graduate course these days. Based on prior performance and off-season addition and subtraction, here are the five defenses we believe will provide the most headaches to opposing offenses in 2013.

Seattle Seahawks

The Seahawks ranked first in the NFL in points allowed in 2012, and fourth in yards allowed. Head coach Pete Carroll and general manager John Schneider have put together a young, aggressive defense based on press coverage and speed to the line of scrimmage. Carroll is the real mastermind here, and he's taken the front packages he learned from Monte Kiffin long ago and expanded them into concepts tailored for today. Seattle runs a lot of what looks to be Cover-1 in a four-man front, but that can change pretty quickly. Former defensive coordinator Gus Bradley (and his replacement, Dan Quinn) will run packages that include 3-4 and 5-2 fronts with alternating safeties and single-linebacker sets.

That said, this defense wouldn't work without the best cornerback duo in the league. If Richard Sherman isn't the NFL's best cover corner, he's on a very short list. Sherman has perfected the art of disrupting a receiver's timing by pressing off the line, and he's as good in trail coverage down the sideline as anyone you'll see. Opposite Sherman is CFL veteran Brandon Browner, who prefers a sledgehammer to his compatriot's finer tools. Browner plays like a safety at the line -- he loves to hit, not just press -- and he's excellent in short coverage.

Seattle's pass rush is the problem going into 2013. Both Chris Clemons and Cliff Avril are battling injuries, and their timelines to return are uncertain. Second-year pass-rusher Bruce Irvin has a more certain return fate, because he'll miss the first four games of the regular season after a suspension for a violation of the NFL's substance abuse policy. Arizona Cardinals castoff O'Brien Schofield might be the main guy through the first few weeks.

San Francisco 49ers

49ers' defensive coordinator Vic Fangio plays a lot of four-man base fronts with two static inside linebackers pre-snap, and he can get away with that, because his defense has as much talent up front as any in the NFL. The right side in particular, featuring Aldon Smith and Justin Smith, is hard to beat. Aldon Smith amassed 19.5 sacks in his second season, but he was shut out in that department after Justin Smith was hurt in a game against the New England Patriots on Dec. 16. That stat speaks to one simple fact -- with all the star power on this team, Justin Smith is the one irreplaceable player. Aldon was greatly assisted by Justin's unique ability to take up double teams with root strength, and slice through them with amazing quickness. As Matt Maiocco of CSN Bay Area detailed, the 49ers gave up 183 passing per game and allowed a 74.6 passer rating when Justin was healthy, and 300 passing yards per game and a 102.1 passer rating when he was not. Justin Smith is healthy now, and he's the key to everything Fangio wants to do.

At the linebacker level, there's a lot of talent -- not only with superstar Patrick Willis, but also with two underrated players in NaVorro Bowman and Ahmad Brooks. Bowman rivals Willis in his ability to play the run and pass, while Brooks in a under-the-radar blitzer.

The question marks here reside in the secondary. The 49ers lost safety Dashon Goldson to the Tampa Bay Buccaneers, and will look to replace him with first-round pick Eric Reid. Carlos Rogers and Tarell Brown are the projected starting cornerbacks, but Rogers is getting up there in years, and Brown is currently working with the team to recover a $2 million contract escalator. Veteran Nnamdi Asomugha is the wild card, but none of this matters too much if anything happens to Justin Smith. His presence or absence will decide whether this defense is great or merely average.

BURKE: 49ers looking for cornerbacks to step forward

Green Bay Packers

After the Packers' Super Bowl championship season of 2010, general manager Ted Thompson allowed defensive lineman Cullen Jenkins to walk in free agency and sign with the Philadelphia Eagles. Green Bay's run defense has never been the same since, despite an impressive amount of talent up front. In the 2013 draft, Thompson selected UCLA's Datone Jones in the first round, and Jones might just have the combination of pass-rush acumen and run-stopping ability that once made Jenkins so special in Dom Capers' defense. That's an enormously important hope for a front that could feature Clay Matthews, B.J. Raji, Jones, and Nick Perry, and if Perry steps up in his second season, Green Bay's defense could approach its offense in productivity, and that might be just what the Packers need for a return trip to the biggest game of all.

Charles Woodson punched his ticket back to Oakland, but there's still a lot of underrated talent in the secondary. Casey Hayward led all rookies with six interceptions in 2012, Tramon Williams is looking to rebound from a season in which he never felt truly healthy, but still played well, and safety Morgan Burnett is a perfect example of the kind of variable defensive back so crucial to Capers' schemes. He can play the deep, centerfield safety spot, as well as at the line of scrimmage. He even matched up in the slot with the Rams' explosive rookie Tavon Austin during the Packers' preseason matchup with St. Louis.

KING: Clay Matthews on defending the read-option

The Houston Texans are stacked on defense. (Bob Levey/Getty Images) The Houston Texans are stacked on defense. (Bob Levey/Getty Images)

Houston Texans

When one talks about the Texans' defense, one must of course begin with J.J. Watt, whose 2012 season may have been the most statistically impressive for any defensive lineman in recent league history. Not only did Watt lead the league with 20.5 sacks -- a preposterous total for a player who spends a lot of time taking double teams from interior linemen -- but he was a total force against the run and an absolute terror for quarterbacks looking to throw footballs over his enormous wingspan. What can he do for an encore? Well, just about anything he wants, it would seem, but the good news for the Texans is that linebacker Brian Cushing, lost for all but five games last season to a knee injury, is back and healthy. Johnathan Joseph and Kareem Jackson lead a secondary with all the talent to be elite, especially if Ed Reed can find some of that old magic down the stretch.

BENOIT: Texans need supporting cast to step up for Houston to be contenders

Chicago Bears

The Bears finished first overall in Football Outsiders' opponent-adjusted metrics last season, but two off-season alterations are fairly major. Second-round rookie Jon Bostic is the favorite to replace Brian Urlacher at middle linebacker, and defensive coordinator Mel Tucker is the man calling the shots in place of Rod Marinelli. The Bears were always great defensively through the Lovie Smith era, but with Smith out and Marc Trestman entrenched as the head coach, Chicago's defense might be looking for a bit of a new identity.

Right now, that identity -- really, the face of the Bears' defense -- is cornerback Charles Tillman, who had yet another great season in 2012. At age 32, when many at his position are slowing down if not on the way out, Tillman led the NFL in forced fumbles and maintained his standing as one of the league's best pass defenders. He and Tim Jennings comprise a cornerback duo that can do just about anything. Julius Peppers is the rock star up front, but don't sleep on Corey Wootton and Henry Melton, two of the more versatile and underrated linemen in the NFL.

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