After a disappointing season last year, the Nationals have made some big changes, but Thomas Boswell thinks the newfound maturity of the players will keep them from repeating last year's mistakes. (Whitney Leaming/The Washington Post)

For two seasons, the Washington Nationals have watched an emerging trend in the importance and construction of big league bullpens. And they have been on the wrong side of history both years. The answer to their problem, they hope, is Ross Detwiler, though he could be forgiven if he loathes the decision to send him to the bullpen.

In recent years, top teams, especially the St. Louis Cardinals and Atlanta Braves, have sent waves of hard-throwing relievers at foes, including the Nats. Not the traditional two or three but four and five, each spewing smoke or darting trick pitches.

To an established starter such as Detwiler, the bullpen may seem like purgatory, a limbo where he may be just the fourth- or fifth-most important contributor. “It caught me by surprise,” Detwiler said. Like Wile E. Coyote and the anvil.

But almost all the Nats see it differently.

“This is something that is going to make us better this year,” Jayson Werth said. “Game 5 of the Division Series against the Cardinals — that’s the example [of how Detwiler could help as a reliever]. We got a 6-0 lead off their starter, but they brought one guy after another out of the pen who threw close to 100 miles per hour, and we only scored one more run.”

The Post Sports Live crew debates which single player is most important to the Nationals’ overall success in 2014. (Post Sports Live/The Washington Post)

Last season, bullpen depth consistently allowed the Braves to stay close in the middle innings, so their dominant back-end relievers could match up with the none-quite-as-good Nats relievers in long, close games. The Braves’ six best relievers had a combined ERA of 2.21 over 367 innings. No Nats reliever was that low; just two were better than 3.10.

“The bullpen has become more important than anyone ever thought it would be,” said Ryan Zimmerman, pointing out that stricter testing for performance-enhancing drugs has “changed the game. You don’t see as many guys who can go 220-plus innings and throw 95 every time out. So you go to the bullpen more and earlier.”

Some top teams have put more high-quality arms in the bullpen even if that hardly maximizes the earning potential of those pitchers, with Detwiler a prime case in point.

“Everybody wants to be a starter. Nobody wants to go to the bullpen,” Nats reliever Craig Stammen said. “For Tyler Clippard and me, it was our last resort. For Detwiler, that’s not the case. He has the chance to go from what the stats would probably say is an average starting pitcher to maybe an elite reliever. You never know how a season works out. He might be in the bullpen for a week, or he might be our late-inning dominant playoff lefty. He’s got a very high ceiling.”

Detwiler’s pitching profile has unique features — all positive — that drove this decision. In a sense, his virtues — and his potential as a reliever — led to a decision that any lifelong starting pitcher loathes. Tanner Roark pitched effectively as a reliever at times last year. Taylor Jordan has no history there at the MLB level. But Detwiler has been menacing, especially against lefties, on his brief trips to relief.

“Go on say it: ‘a 6-foot-5 lefty who throws 95 miles per hour with a crossfire delivery,’” Manager Matt Williams said after Detwiler’s first impressive relief appearance Wednesday night. “There aren’t many of those . . .

“I saw aggression. That’s what I want. That’s what I like. And he got two outs on breaking balls. . . . We see him as that power lefty like Justin Wilson in Pittsburgh.”

Since Wilson’s ERA was 2.08 last year, one of the best in the majors, the bar is being set high. The Nats wonder whether Detwiler’s sinker will be even faster if he’s pitching just an inning or two per outing.

Detwiler knows the relief drill: “Out of the ’pen, you must attack or you are out of there before you know it.” Detwiler relies on only one pitch: that sinker he threw 88 percent of the time last season. That haunted him the third time through opposing batting orders. Now, not a problem.

Many assume the Detwiler call was Williams’ first symbolic act of authority. The Nats, including Detwiler, sense that the move was the result of an organizational analysis, though Williams certainly could have dictated a different outcome if he felt strongly.

“These decisions are made by a lot of people. It’s about ‘team first.’ Everyone wants to win,” said Zimmerman, who’s doing his part by learning to play first base occasionally.

All offseason the Nats tried, inconspicuously, to add one more hard-throwing arm to go with Rafael Soriano, Clippard, Drew Storen, Stammen and finesse lefty free agent Jerry Blevins. They thought they had lined up standout right-handed free agent Grant Balfour for a two-year deal, but internal delays about pushing salary into future years may have let that deal slip away. Now, as two veteran Nats pointed out, Detwiler in a sense becomes Balfour — the reliever with two years of team control who may pitch himself into a bigger ’15 role. Even better: Detwiler is left-handed.

One last element played in the Nats’ decision and may have sealed it. Few teams match Washington’s pipeline of starting pitching. You have to find out what you’re holding. After 69 starts, Detwiler is known: 3.46 ERA the past three years but with injuries that have kept him to only one season with at least 75 big league innings. A.J. Cole, 22, didn’t give up a run in major league spring training. Lucas Giolito, 20, if healthy, is in a future rotation. So, logic says, find out what Roark or Jordan can do with a rotation shot.

“The job Tanner Roark did last year, he just ran through big league lineups by throwing strikes. Guys got a lot of bad ‘takes’ against him,” said Werth, meaning that identifying Roark’s pitches confused even good hitters.

All plans have glitch potential. Changing a pitcher’s routine from starter to reliever — once — is standard practice. Switching back and forth is dangerous. If early season injuries leave the Nats’ rotation shorthanded, do you wave for Detwiler when you know the grand plan prefers him in the bullpen?

For now, the Nats are following Williams’s mantra of the spring: aggression in all things. The most effective Nats team over a full season and in the playoffs has Detwiler in the bullpen. “If we’re celebrating at the end of the year, I’ll be really happy about the move,” Detwiler said. He didn’t say how he’d feel if they are not.

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