Redskins nose tackle Barry Cofield, here sacking Eagles quarterback Nick Foles along with Brandon Meriweather, is a key to their 3-4 defense. But he’s 30, an age after which players don’t often improve. (Toni L. Sandys/The Washington Post) (Toni L. Sandys/The Washington Post)

Four seasons after the Washington Redskins switched to a 3-4 defense, they’re still waiting for the move to pay off. They’ve experienced big problems up front.

Last fall, the line was among many weak links on a defense that surrendered 29.9 points per gametied for 30th in the 32-team league. Redskins President and General Manager Bruce Allen is banking on former Dallas Cowboys lineman Jason Hatcher to bolster the unit, but the Redskins appear to need more help along the line than one high-priced newcomer can provide. Unless several holdovers experience turn-back-the-clock seasons — which seems improbable because of their age — the Redskins most likely will continue to struggle in an effort to become something they strive to be: a good 3-4 defense.

Not surprisingly, Coach Jay Gruden expressed optimism about the line on the first day of minicamp. The Redskins have “multiple players that can come in and rotate to make sure we stay fresh,” Gruden said Tuesday at Redskins Park. “We’re not just limited to two or three or four guys.”

Of course, some players are more important than others. For the line to be effective, nose tackle Barry Cofield figures to be the key. Despite being undersize for his position at about 300 pounds (the best nose tackles are listed in the 330-pound range), Cofield has been the unit’s most productive player and leader since he joined the Redskins in free agency before the 2011 season.

NFL defensive coaches have a saying: If you don’t have an effective nose tackle, you don’t have a 3-4 defense. For a 3-4 alignment to succeed, nose tackles must engage multiple offensive linemen, which, in theory, frees linebackers to make plays. Although it’s also important for defensive ends to occupy the players opposite them in the 3-4, nose tackles are the foundation. Until last season, Cofield provided a solid one.

Early last fall, Cofield played well overall. Later in the season, offensive linemen often moved him around, said a NFC East defensive assistant who has studied tape of the Redskins. Cofield wore down while playing too many snaps.

Recovering from hernia surgery, Cofield has been limited in offseason practice. The Redskins expect Cofield to be at full speed for the start of training camp on July 24, and they’ll need him to be better against the run.

In the Redskins’ locker room, no one is more respected than the hard-working Cofield, “who always gives this team everything he has,” outside linebacker Brian Orakpo said recently. “Man, when you see how he works, you know he’s gonna push himself to help us be the best we can be. . . . Maybe people outside [have doubts] about him. We don’t.”

But Cofield is 30. NFL history tells us that linemen, after a career’s worth of collisions, generally don’t improve after that age. In the Redskins’ line rotation, there could be four players who are at least 30: Cofield, Hatcher , Stephen Bowen , who’s recovering from knee surgery, and Kedric Golston . And the youngest member of the group has been the biggest disappointment.

A second-round pick in the 2011 draft, Jarvis Jenkins, 26, was expected to quickly become a fixture at one end spot. A knee injury cost Jenkins his entire rookie season, and Jenkins last season was suspended for the first four games for a violation of the league’s policy on performance-enhancing substances. When he has played, Jenkins hasn’t made enough plays. Too often, he struggles to get off blocks, the NFC East assistant coach said.

Chris Baker, who turns 27 in October, was rewarded with a nice contract after having the best year of any lineman. Hatcher got a big deal — he’ll have a salary of $10.5 million this season — to re-energize a line that produced only 51 / 2 sacks a season ago.

Hatcher, who had a career-high 11 sacks in his final season for Dallas, has impressed in practices, leaving no doubt “he was a great guy to bring in,” cornerback DeAngelo Hall said recently. “He’s gonna help the pass rush, which will help [the secondary]. He’s gonna help the run game. He’s just gonna give us more depth. That’ll make it easier on all the guys.”

Gruden and defensive coordinator Jim Haslett hope so.

With less mileage than the other linemen, Baker and Jenkins are the most likely candidates to improve. If Hatcher draws double teams, as expected, Baker and Jenkins could face single coverage. In those situations, they must deliver by pressuring the quarterback.

Hatcher also has been productive rushing the passer in a 4-3 alignment. No team maintains one front on every play. Over the past four seasons, the Redskins have shown a 4-3 front at times. They’ll likely do it more to make Hatcher most comfortable to pursue the quarterback.

But it’s not just about sacks. In 2011, the Pittsburgh Steelers, who provided the model for the Redskins’ 3-4 defense, led the NFL in total defense and passing defense despite finishing tied for 17th in the league with 35 sacks. In this age of fast-paced, spread offenses, getting the quarterback out of his comfort zone with consistent pressure is almost as important as recording sacks, the NFC East assistant coach said. Gruden buys that line of thinking.

“You want to keep those guys fresh with the no-huddle attacks,” Gruden said. “You’re going to have to have different defensive linemen in there rotating, playing at a high level. . . . The more the merrier as far as guys rushing.”

On defense, the Redskins know exactly who they want to be. It’s up to the line to finally establish its identity.

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