Richard Sherman, Luke Kuechly among indispensable defenders

Dallas Cowboys linebacker Sean Lee tore his ACL during last Tuesday's organized team activity and appears to be done for the season. It's a crippling, devastating blow for an already-thin, rebuilding defense. Lee's irreplaceable. This changes the feel of the season (and the potential win total) in Big D.

Then, on Friday, the Arizona Cardinals were dealt a gigantic blow of their own, as linebacker Daryl Washington was suspended for at least one year after violating the league's Policy and Program for Substances of Abuse. I've been talking up this team as a potential contender all offseason -- and Bruce Arians has publicly discussed the possibility of being the first host team to make the Super Bowl -- but this development hits hard. While he might not be a household name nationally, Washington is a star. In fact, last year at this time, I listed him as one of the nine most indispensable defensive players in the NFL.

In the wake of those two crushing losses, it feels like the right time to go back to that well -- to identify the most vital defensive pieces across the NFL.

Now, before you digest this list, understand one thing: This is NOT (all caps, bold, italics) a ranking of the NFL's best defensive players. For the second straight year, J.J. Watt won't appear on the list. Watt had another strong season in 2013 ... and the Houston Texans won two games. Meanwhile, I couldn't separate Tampa Bay Buccaneers stars Gerald McCoy and Lavonte David in terms of overall importance. The same goes for Kiko Alonso and Mario Williams in Buffalo, as well as Vince Wilfork, Jerod Mayo and Darrelle Revis in New England. The San Francisco 49ers are so loaded on the defensive side of the ball that I can't logically narrow it down.

The crack editorial staff at NFL.com simply asked me to name the defensive players "you cannot afford to lose." Here's my Schein Nine:

1) Richard Sherman, CB, Seattle Seahawks

He's right. Sherman's the best cornerback in the NFL, headlining the best defense in the NFL. And the "Legion of Boom" has changed a bit. Corner Brandon Browner and underrated nickelback Walter Thurmond left the team via free agency.

While Earl Thomas and Kam Chancellor comprise the NFL's top safety combination (I voted both first team All-Pro in 2013), Sherman makes the defensive backfield tick. In addition to his timely play, knack for creating turnovers and leadership, Sherman spearheads the Seattle swagger. The Seahawks wouldn't be the Seahawks without him.

2) Luke Kuechly, MLB, Carolina Panthers


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Cam Newton gets more headlines, but Kuechly is Carolina's MVP, the heart and soul of the Panthers. The 2013 AP Defensive Player of the Year -- yes, he got my vote -- is totally irreplaceable. The pure numbers (156 tackles, four interceptions, two sacks) speak volumes, but he's also the lead dog of a unit that finished last season at No. 2 in total and scoring defense. Meanwhile, Newton's offense ranked 26th and 18th, respectively, in the corresponding categories.

Kuechly's non-stop motor and highly advanced football IQ set the tone for this D.

3) Robert Mathis, OLB, Indianapolis Colts

Unlike the two guys listed above, Mathis does not play on a dominant defense. For the most part, Andrew Luck serves as the ultimate deodorant for Indy's D. But one thing the unit did reasonably well last season was get to the quarterback, thanks to the NFL's reigning sack king. With 19.5 sacks on the year, Mathis was a one-man wrecking crew. And this is nothing new -- the 33-year-old has been an elite pass rusher for years.

Of course, Mathis has been suspended for the first four games of the upcoming season for violating the league's performance-enhancing drug policy. This is no small issue. Indy has to face two of the league's most prolific offensive teams -- the Denver Broncos and Philadelphia Eagles -- in the first two weeks of the season, and both games will be on national television. Remember how Mathis terrorized Peyton Manning last year? This suspension could affect the Colts' seed in the postseason. It's that big of a deal. Indy needs Mathis to come back with a vengeance in October.

4) Geno Atkins, DT, Cincinnati Bengals

When the defensive tackle went down with a torn ACL last October, the Bengals' defense lost its bite. There's no defensive lineman more important to his team. It's not even close. That's why he topped this list one year ago.

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Atkins might not be ready for the start of the season. When he does return, will he resemble the dynamite player he's been in the past? These Bengals need that guy back -- that's the guy who's indispensable. If Geno Atkins isn't Geno Atkins in 2014, the Bengals fall short. With Andy Dalton at quarterback, the team's success rides on the defense being dominant -- and that will ride on No. 97.

5) Muhammad Wilkerson, DL, New York Jets

The Jets' offense was offensive last season. While it should be better with Chris Johnson and Eric Decker in the fold, Rex Ryan's team relies on its defense. Gang Green was solid in that area last year, ranking third against the rush and sparking a surprising 8-8 campaign. This was due in no small part to Wilkerson, who blossomed into a star in his third NFL season. Sure, the 2011 first-rounder racked up 10.5 sacks, but he also established himself as a great run stuffer, versatile player and true leader.

The Jets' defense has legit questions marks. Still, this 315-pound force of nature gives the unit a chance to be great.

6) Robert Quinn, DE, St. Louis Rams

Jeff Fisher is a great coach, and the Rams have strong talent and depth all along the defensive line. Don't let any of that fool you, though: Robert Quinn is the straw that stirs the drink. He is a beast, sacking the quarterback 19 times last year.

The Rams play in the NFC West -- the toughest division in pro football. Sam Bradford can't stay healthy at quarterback. Quinn is a man St. Louis simply can't live without.

7) Clay Matthews, OLB, Green Bay Packers

While Aaron Rodgers is everything to this team, if the goal is to win a Super Bowl, Rodgers and Co. need the defense to help the cause.

Matthews missed time in each of the past two seasons, and Green Bay felt his absence. He's still recovering from two separate surgeries on a broken thumb that sidelined him for six games last season, including the playoffs. The four-time Pro Bowler told the local media last week he plans to be ready for the beginning of the season. If coordinator Dom Capers' defense plans on generating a pass rush, Matthews had better be.

8) Joe Haden, CB, Cleveland Browns

Cleveland's defense is ready for prime time under first-year head coach Mike Pettine. The talent, the coaching, the scheme -- it's all there. Pettine loves his cornerbacks, which is why he selected Justin Gilbert with the team's first pick last month -- before the Browns took Johnny Manziel. Gilbert is a fine young prospect to pair with an established stud at the position. Yes, I think Haden is an elite corner.

Between Johnny Football getting acclimated to life in the NFL and receiver Josh Gordon's uncertain status for 2014, the defense needs to carry the Browns. It all starts with Haden, who is clearly the team's best player on that side of the ball.

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9) Brian Orakpo, OLB, Washington Redskins

Perhaps this isn't said enough, what with the high-profile quarterback and the shiny new toy at receiver, but Brian Orakpo is the best player on the Washington Redskins. Period. All hope is gone if something happens to the sack master.

Follow Adam Schein on Twitter @AdamSchein.