Twenty years ago, Pete Carroll’s name was a punch line. Following the 1994 season, the New York Jets fired Carroll after one year as head coach. It wasn’t simply that Carroll’s team lost; it was how it lost. The ’94 Jets started 6-5, then crashed, losing their final five games amid a series of lifeless performances. The collapse began with a last-second loss on one of the most famous plays in NFL history: After leading the Dolphins back from a 24-6 third-quarter deficit, Miami’s Dan Marino brought his team to the line with just less than 30 seconds remaining. Marino signaled that he was going to spike the ball to stop the clock ­ ­— then didn’t. Instead, he rifled a touchdown pass to Mark Ingram, pushing the Dolphins to a 28-24 win. The lasting image from the Jets’ 1994 season was of a motionless Carroll gazing blankly at the field as the Dolphins celebrated Marino’s ruse.

Carroll got another shot at being a head coach after two seasons as a defensive coordinator, this time in New England. He lasted three years before the Patriots fired him. He spent most of 2000 essentially out of football, doing some consulting, some media, and even writing a few online sports columns. USC hired Carroll as head coach in December 2000, a decision that sparked a combination of derision and apathy; Carroll, who was the Trojans’ fourth choice following a frantic coaching search, is lucky the Internet commentariat wasn’t as robust then as it is now.

Then something unexpected happened: Carroll started winning, and kept winning. Since 2001, Carroll’s college and NFL teams have posted a 121-45 record, including the Seattle Seahawks’ 24-8 mark over the last two seasons.

Coaching is a hard profession. It certainly has its rewards, as skyrocketing salaries for NFL and college head coaches illustrate, but failure is the norm. Being a coach means eventually getting fired, and making a career out of coaching at all is an accomplishment. Carroll, however, has done something especially rare, pushing through wrenching public failure to succeed beyond all expectations. A coach can’t do that without learning from past mistakes, and Carroll has certainly changed for the better.

Much of the credit goes to Carroll’s defense, which has been the foundation of his success and remains closely tied to the first lessons he learned as a very young coach. “To be successful on defense, you need to develop a philosophy,” Carroll said at a coaching clinic while still at USC. “If you don’t have a clear view of your philosophy, you will be floundering all over the place. If you win, it will be pure luck.”

Carroll’s Seahawks, who face the San Francisco 49ers in Sunday’s NFC Championship Game, don’t win with luck. They win by physically dominating opponents and playing championship-level defense. They also win thanks to Carroll’s new spin on an old scheme.

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After spending a year selling roofing materials in the Bay Area, Carroll got his start in coaching in the 1974 season as a graduate assistant at his alma mater, the University of the Pacific. His big break came in 1977, when he secured a GA job at the University of Arkansas under new head coach Lou Holtz and defensive coordinator Monte Kiffin. Carroll later called that job “the best thing that ever happened” to him.

Most graduate assistants simply want to break into coaching; Carroll got that, but he also got something else: an ideology. “I am an example of a person who got zeroed into a philosophy early,” said Carroll. “Monte ran what is known in coaching circles as the 4-3 Under defense … That was the first time I started to get hold of something that had a philosophy to it. I started to grow with the defense.”

Taken literally, “4-3 Under” refers to a particular personnel grouping — four defensive linemen and three linebackers (hence “4-3”), and by extension four defensive backs — where the defensive linemen align away from the offense’s strong side (hence “Under”) while the strongside linebacker positions himself on the line, usually right across from the tight end. This is the same structure Kiffin ran while working for Tony Dungy and the Tampa Bay Buccaneers, and the “Under” front remains popular in the NFL today.

Carroll has never exclusively relied on this scheme; instead, he viewed Kiffin’s 4-3 Under less as a particular alignment and more as a belief system about football. “I have been running that same base defense since 1977 when I learned it from [Kiffin],” Carroll said at a coaching clinic. “I have used variations of this defense my entire career. I have stayed with its principles through all my years of coaching.” And the overarching principle is simple: Be aggressive.

The key to being aggressive is something called “one-gapping.” “There are really two [defensive] philosophies in pro football,” former Tampa Bay and Indianapolis head coach (and 4-3 Under guru) Dungy said at a lecture for coaches. “Do you want to be a one-gap team or a two-gap team?” Used this way, “gap” simply refers to the space between offensive linemen, and “run fits” is coach-speak for how a team handles those gaps.

The need to choose between one-gapping and two-gapping arises, according to Dungy, “because of simple math: You have eight gaps to fill and you only have seven front players.” A one-gap technique is much like it sounds: Each defender is responsible for attacking and controlling his assigned gap. By contrast, a two-gapping defender is responsible for the gaps on either side of the lineman across from him. How? He controls both gaps by controlling the blocker in between. A one-gapper attacks gaps, while a two-gapper attacks people.

Carroll, like Dungy, prefers not to two-gap. The problem isn’t the theory — a potential two-for-one where a single defender can clog up two running lanes is a great deal for the defense — but rather that two-gapping too often results in hesitant defensive linemen who try to read and react and thus fail to disrupt the offense.

“When you put a defensive lineman in a gap and tell him he has to control the gap, he can play very aggressively,” Carroll said at a coaching clinic.

“We want to be an attacking, aggressive football team,” he said at another clinic. “We don’t want to sit and read the play like you often have to with two-gap principles of play.”

Of course, that doesn’t address Dungy’s math problem: the unaccounted-for eighth gap. The one-gap answer is to use a safety to fill the void. “We assign everyone a gap and use an eighth man out of the secondary to cover the eighth gap,” Dungy explained at the lecture. “Our system has not changed in about 20 years.”

If you watch Carroll’s Seattle team, you’ll see all of this at work: aggressive one-gap techniques, safeties rocking down to help against the run, and that classic 4-3 Under front. But that’s not all you’ll see.

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Sandwiched between his failed stints with the Jets and Patriots, Carroll served a successful two-year run from 1995 to 1996 coordinating a talented San Francisco 49ers defense. He coached some great players, including safeties Merton Hanks and Tim McDonald as well as linebacker (and current Seahawks assistant coach) Ken Norton Jr. Those players, coupled with defensive line coach Bill McPherson’s experience, allowed Carroll to experiment with new wrinkles and put together a comprehensive defense that had answers for almost anything an offense tried. Carroll told the Seattle Times that the defense he ran in San Francisco represented “the ultimate package.”

Although Carroll used bits of that system with New England, he never got it fully up and running, and it was simply too much for college players, even the very talented ones at USC. “I was the defensive coordinator and putting the whole thing together [at USC], but our guys just couldn’t handle it,” said Carroll. “It was just too much stuff, and it was too much for the coaches.”

Carroll’s Seahawks are a different story. In Carroll’s first season with Seattle, his team ranked a dreadful 25th in scoring defense and 27th in total defense. The Seahawks jumped to seventh and ninth, respectively, the next year, though, and haven’t looked back since, finishing first in both categories this season. The biggest reason is the job Carroll and general manager John Schneider have done in revamping the roster. Not far behind, however, is the implementation of new wrinkles to Carroll’s base defensive system, with many pulled from his days in San Francisco.

Specifically, Carroll often calls for at least one defensive lineman to two-gap in an effort to get the best of both worlds: With one or two linemen two-gapping to clog additional running lanes, the remaining defenders are free to attack their gaps or drop into pass coverage. Hybrid defenses that can steal back a gap have become increasingly necessary as modern offenses tilt the arithmetic in their favor by using the quarterback as a running threat in the read-option.

In addition to Carroll’s tactics, the Seahawks’ personnel dictate changes. Seattle’s defense is talented, but it’s also rather eclectic: Tall and skinny, short and stout, Seattle’s defenders come in all shapes and sizes. As just one example, the Seahawks start 254-pound Chris Clemons at one defensive end spot and 323-pound Red Bryant at the other. But Bryant is a perfect two-gapper, and Carroll often places him directly across from an offensive guard or tackle to blow up running plays to the offense’s strong side.

While these wrinkles trace back to Carroll’s previous NFL stints, he refined the art of adapting them to his talent while coaching college. “That really came out of my time at SC,” Carroll told Seahawks.com. “We forced [young players] to play, in essence. And then we discovered if we asked them to do things they could do uniquely well, that they could elevate faster and find their confidence sooner.”

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Nowhere have Carroll’s adaptations been more successful than with Seattle’s pass defense, led by the so-called Legion of Boom. The unit led the NFL in every conceivable metric this season, which is only surprising given how often the Seahawks use one of the oldest, most basic pass coverages in all of football: Cover Three. And they don’t simply use it; they use it to shut opponents down.

Also known as Three-Deep zone coverage, Cover Three is a fundamental defensive building block; almost every high school team in the country runs some version. As the name implies, three defenders drop and divide the field into three deep zones — typically the two cornerbacks on the outsides and the free safety in the middle — while four other defenders drop to defend underneath passes as the remainder rush the QB. This coverage is sound against the pass and allows an extra defender to come up to stop the run, but it’s also conservative, which is why veteran NFL quarterbacks tend to carve it up and thus why it’s not commonly used in the NFL on passing downs.

All of the basic elements are there when Seattle runs Cover Three, but the subtle tweaks make it deadly. Carroll often brings strong safety Kam Chancellor near the line as essentially another linebacker, while all-everything free safety Earl Thomas roams deep center field, instinctively breaking on passes or flying up to stuff the run. (Carroll is not afraid to reverse those roles, however.) While at USC, Carroll described his ideal free safety as “a natural player” that “you don’t have to coach” much. Thomas is all that and more, but the real key is that Carroll keeps things simple for his star. “If you have a million reads for your secondary, you are crazy,” Carroll said at a coaching clinic. “At the highest level in the NFL, the pass game is as complex as you can imagine. However, if [the free safety] can play the post and the seam route, then they can learn to play at that level.” Thomas, it’s safe to say, can play the post and the seam.

As good as Seattle’s safeties are, however, its cornerbacks are even more crucial, particularly former fifth-round pick and converted wide receiver Richard Sherman. Now the best cover corner in the NFL, Sherman was an afterthought on every NFL team’s draft board, including Seattle’s.

“[Sherman]’s a guy I watched on film that we weren’t even thinking about much,” Carroll said. “But then I saw him playing press and tackling, and knew him as a receiver coming out of high school, and thought, ‘Oh boy.'”

Sherman’s skills allow Carroll to put his spin on old, conservative Cover Three: While this is zone coverage, Seattle’s cornerbacks play tight press coverage on the outside wide receivers as long as a receiver’s initial steps are straight downfield. Notice the coverage drops from the underneath defenders in the GIF below: This is a zone defense all the way, except for those press corners.

Carroll’s defense provides all of the benefits of traditional Cover Three — namely a deep middle safety and excellent run support — without conceding easy throws. Cover Three is as old as the forward pass, but Carroll’s Seahawks have made it modern by making it their own. And the result has been the best pass defense in the NFL in more than a decade.

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The Carroll who coached the Jets and Patriots wouldn’t have been able to build and maintain the kind of team he now has in Seattle. He had the schemes, but he hadn’t yet mastered their application. Carroll has evolved over time by turning earlier failures into lessons.

Interestingly, Carroll’s own description of this evolution is somewhat paradoxical: “There is no offensive play calling or defensive scheme that is going to win championships for you. It is how you can adapt and adjust to making the schemes work. The only way you can do that is to have a strong belief system [emphasis mine].”

That explanation might only make sense to Carroll, a man who counts both John Wooden and Jerry Garcia among his primary influences. Carroll thinks his unshakable belief in those early lessons from Holtz and Kiffin have enabled him to evolve those ideas and adapt them to the present, and, most importantly, to improve as a coach. In the spirit of that seeming paradox, here’s one of my own: Pete Carroll, the coach who succeeded through failing.