Rooke linebacker Ryan Kerrigan has shown an ability to master the details of a complex NFL defense. (John McDonnell/The Washington Post)

Three Fridays ago, indecipherable hieroglyphics littered the whiteboards that cover the walls of the defensive meeting room at Redskins Park, non sequiturs scattered everywhere – “gold” and “rip” and “liz” and “lamb.” The season hadn’t yet started.

All this apparent confusion — 21 different coverages and 38 different blitzes, and that’s just in the Washington Redskins’ “sub” package, used mostly on third downs — had to be drilled and distilled by all 25 defensive players, from 14-year veteran London Fletcher to one rookie, a starter from the day he walked in the building. Never mind that he wasn’t a month past his 23rd birthday.

“I think I’m ready,” Ryan Kerrigan said that day. “But I guess I won’t know till I do it.”

The combinations of letters and numbers on those whiteboards — all the blitzes and coverages the Redskins would employ against the New York Giants in the season opener, perhaps 70 percent of their overall defensive playbook — represented the essence of the 3-4 defensive scheme employed by Washington Coach Mike Shanahan and his defensive coordinator, Jim Haslett. But they also represent the current state of professional football.

The NFL, in its 92nd season, has never been more complicated. Thirty years ago — when Shanahan was still coaching in college and Haslett was still playing linebacker in the NFL — offenses altered their formations only nominally, and defenses played almost exclusively man-to-man coverage. There weren’t systems that ran four receivers and no running backs on one play, two running backs and two wideouts on the next, dictating drastic defensive changes. Defenses didn’t counter with expertly disguised zone blitzes, with basketball-style coverages in which a linebacker might hand off his responsibility for a receiver to a safety, with packages using as many as six defensive backs. Game plans were built more on broad concepts — maybe we’ll throw more than usual, maybe we’ll run more to the right, but we’ll sure as heck perfect what we do — than on carefully dissected analysis, on scripts and playbooks that, each week, run hundreds of pages.

“If you really sat down and looked at the video then compared to now,” Shanahan said, “you’d almost just laugh at what you’re able to do now.”

Into this world, not two months ago, stepped Kerrigan, a chiseled-from-granite pass rusher — 6 feet 4, 267 pounds, his does-he-even-shave-yet face obscuring maturity that those who know him back home in Indiana believed would help his transition.

“He’s just a sponge,” said Gary Emanuel, the defensive line coach during Kerrigan’s senior season at Purdue.

“His football IQ, it just helps him fit in so quickly” said John Hochstetler, his coach at Muncie Central High.

No draft pick, for any team in any round, is chosen without considering such characteristics. Outside linebacker, in the Redskins’ scheme, “is probably the toughest position to play — mentally,” Shanahan said. As the Redskins screened players they might select with the 16th choice in last April’s draft, they brought in Kerrigan for a tour of Redskins Park and, essentially, a job interview. He had been a defensive end in a 4-3 alignment — four down linemen and three linebackers — all through college. Would he be able to handle all the Redskins would ask of him — adjusting to a new strategy, a new position, a new life?

Haslett got him for 30 minutes, long enough to sling pieces of the Redskins’ defense at him. He taught him a few basic concepts and the terminology. Then he quizzed him.

“What’s hot?” Haslett said. “Rip, rip, rip!”

“I rush,” Kerrigan responded.

“Liz!” Haslett said.

“I’m dropping, but I don’t know what ‘quarters’ means,” Kerrigan said. He couldn’t know it all. Instantly, though, he mentally fit himself in as a linebacker in a 3-4. For 30 minutes, he mentally became a Redskin.

“In a half-hour, he knew all this stuff I’m talking about,” Haslett said. “In a half-hour. I could do that with another player, with a veteran, and they still wouldn’t know. It’s so much to know.”

A full year to learn

“Oh, man,” Kerrigan said. “Oh, no.”

He lowered his head, almost embarrassed. It was the final week of August, and the only light in the auditorium at Redskins Park came from two screens — the small one only a couple of feet from Kerrigan’s face, and a full projection at the front of the room. Both showed the same thing: Kerrigan, playing in his third preseason game in the NFL, figuring out the complexities of his new job.

“I’m just thinking too much on this play,” he said.

The film showed the Redskins playing in Baltimore, the first few minutes of a scoreless game. Because he would sit out the exhibition finale the following week, this was his last chance to take what he had learned in his book study and the film room and the practice field into the kind of situation he would face during his rookie year.

“See, at the start, the offensive tackle steps down,” Kerrigan said, his hand on a controller that could slow down the play, that could flip the view from the sideline to the end zone. “When he does that, I’m thinking it’s a run away [from his side]. But . . . ”

He sighed again.

On every NFL play, there are moments like this, 11 defenders peering across the line of scrimmage and deciding what will happen next. Television can’t begin to capture the complexities with which players are dealing at an increasingly rapid pace. At Kerrigan’s position, each play brings three possibilities: stop the run, rush the passer or — and this is the most foreign to him — drop into pass coverage.

“We ask him to do three different activities,” said Lou Spanos, the Redskins’ linebackers coach, “and in a matter of a second, after the ball’s snapped, to diagnose what’s going on, to do his reads and execute whatever the defense asks him to do.”

On the first day of training camp, Kerrigan suffered a bone bruise to his right knee and missed more than a week of practice. When he returned, even before he could participate fully, he began taking the field early and working with Spanos. Each day, the Redskins would install a portion of their defense — short yardage, or a third-down blitz, or something else. And each day, Kerrigan would pantomime his actions at Spanos’s request, before his teammates had begun their workout. He lined up against a blocking dummy, and sprinted inside. He went back to the line of scrimmage, and did it again.

“To be honest, it hasn’t been extremely overwhelming,” Kerrigan said one day after practice. “It’s just, I need to do it more, just actually practice it more. It has to come to where it feels natural.”

Feeling natural in one aspect of the defense, though, doesn’t mean he would feel natural in all of it. In the Redskins’ “sub” package — from which they’re likely to blitz the most — Kerrigan and the other outside linebacker, Brian Orakpo, effectively become the defensive ends.

“They have to learn both positions,” Haslett said last week. He approached Orakpo, who sat on a couch outside the Redskins’ locker room. “’Rak, how hard is this defense to learn for you guys?”

Unlike the defensive linemen, the outside linebackers aren’t rotated out. They might end up tangled up with a tackle in the offensive backfield. They might end up 20 yards downfield with a tight end, or even a running back. Because they’re defensive ends in certain situations, they have to learn almost twice as much as other defenders.

“Dang, man,” Orakpo said. “I mean, a full year. It takes a full year.”

Kerrigan, though, didn’t have a full year. With the tape of the play against the Ravens flickering before him, he entered analysis mode. Kerrigan lined up in a two-point stance, his new reality after spending his entire collegiate career with his hand on the ground to start the play. At the snap, Ravens right tackle Michael Oher moved slightly to his left, giving Kerrigan the impression that the play was a run in that direction.

“But I have to have good vision,” Kerrigan said. “I have to see the whole thing.”

The progression for Kerrigan’s eyes, by the Redskins’ rules, goes first to the ball, then to the man directly in front of him — many times, the tight end — then to the tackle, then to a pulling guard or an oncoming fullback. In this case, Kerrigan should have noticed that the tackle’s helmet stayed high. He was standing up, a clear giveaway that it was a pass play.

“It’s a free rush,” Kerrigan said. “I’ve got to take advantage of it.”

By the time Kerrigan realized his error and stepped toward quarterback Joe Flacco, the ball was gone. He saw himself on film the next day, and knew he had let a potential hit on the quarterback — a precious commodity — slip away.

“The best thing about him, though: Nothing fazes him,” Haslett said. “If he screws up, it doesn’t really bother him. He doesn’t make the mistake the second time.”

So as the opener approached, and the 300 pages of the playbook were digested again and again, Kerrigan convinced himself he was ready.

“I feel night and day from when I started,” he said.

‘Too young to know that’

On Sept. 18, the Redskins trailed Arizona by two points with less than five minutes remaining. The Cardinals faced third and seven from their 23. Allow a conversion, and Washington’s chances of winning would dwindle.

As the opponent approaches the line of scrimmage, the Redskins’ defenders have several ways they might communicate to each other about what they think will happen when the ball is snapped. Fletcher, the inside linebacker who is a defensive captain, can call “rabbit” or “bird” or some other keyword determined during a week of practice, something that alerts the entire unit to what might come next.

But as Arizona quarterback Kevin Kolb approached the line of scrimmage, Fletcher simply listened. “You can hear, sometimes, things that might tell you what they’re going to do,” Fletcher said. What he heard from the Arizona linemen indicated to him that Cardinals right tackle Brandon Keith was likely going to crack down to his left, to crash onto Fletcher rather than dealing with Kerrigan.

Instantly, Fletcher turned to his left, and shuffled his hands, yelling to Kerrigan. “He let me know I had to adjust my angle,” Kerrigan said.

By this point in his development, Kerrigan had already arrived. The previous week, he provided the pivotal play against the Giants, shoving an opposing lineman to the ground to avoid a cut block, then instantly moving his hands into the air to deflect quarterback Eli Manning’s pass, which he hauled in and ran nine yards for a tiebreaking touchdown. Earlier in the day against Arizona, he came up with his first sack. He covered the tight end 15 yards downfield, converged with safety Reed Doughty on wide receiver Andre Roberts, and tipped a pass that Fletcher intercepted.

“Some players just have a knack,” Fletcher said later. “He has one.”

With those formalities out of the way, Kerrigan took the signal from Fletcher, and knew his job: Get to Kolb. At the snap of the ball, he sprinted directly upfield, directly at the quarterback. Kolb, about to be engulfed, unloaded quickly. And in an instant, that one subtle pickup within the confines of the Redskins’ defense — Fletcher figuring out that the tackle would crack down on him — turned into another tipped pass for Kerrigan. The Cardinals had to punt. The Redskins kicked the winning field goal on the ensuing drive.

“He’s too young to know that stuff,” nose tackle Barry Cofield said.

When Kerrigan emerged from the shower afterward, he shuffled to his stall in an elated locker room, whistling “Hail to the Redskins,” all but to himself.

“For the most part, everything we saw today on the field we saw in practice,” he said. “After that, it makes it feel almost like second nature.”

It is not — not yet, anyway — completely second nature. Against Arizona, Kerrigan once dropped back to cover the tight end when the play was a run to the opposite side, for instance. “It’s just little things,” Haslett said. “It doesn’t kill you, but it shows you how much you have to learn.”

By Wednesday morning, Kerrigan was in possession of a thick, white binder that sported a picture of Cowboys Stadium on the cover, which read: “Washington Redskins @ Dallas Cowboys, Monday, September 26, 2011, 7:30 p.m., Ryan Kerrigan.” It contained everything that has to be second nature Monday night — the Redskins’ base defense, their sub packages, what the Cowboys have done the past four games in the run game, the pass game, play-action, third down, short yardage, goal line, all of it. A completely new course.

“Everything changes based on who we’re trying to stop,” Haslett said.

Wednesday afternoon, as his teammates climbed up the hill from the practice field back to the locker room, Kerrigan stayed behind, working with Spanos and defensive line coach Jacob Burney. Helmet off, he fought against rookie offensive lineman Willie Smith, refining techniques to use against the Cowboys. He is a physical specimen off to a fine start in his NFL career. But he is also a pawn for Haslett and Shanahan to use as they design more complex elements in an already complex game.

“Sometimes, when you think too much and you game plan too much, you take it out of the players’ hands, and you don’t want to do that,” Shanahan said. “I’ve done that before. I think every coach has. There’s a fine line, letting your players play, and at the same time giving them a game plan where they can be effective.”

By Thursday morning, Kerrigan — all of two games into his NFL career, with a sack, an interception, eight tackles and three defended passes to his credit — had fully immersed himself in the Cowboys. “I think I’ll be ready,” he said.

The clock in the Redskins’ locker room showed 11:29 a.m. His next meeting started at 11:30. He slid on some flip-flops, grabbed his backpack — that massive playbook inside — and hustled upstairs, another lesson to be learned.