Just one season after finishing 31st in ERA, the Seattle Mariners’ bullpen has been one of the best in the majors in 2014.

Seattle’s relievers own a collective 2.49 ERA, trailing only the San Diego Padres for the top spot in the league. If they finish the year with that number, the Mariners will have posted the second-best bullpen ERA of any American League club in the designated hitter era, trailing only the 2.35 put up by the 1990 Oakland Athletics.

That impressive number includes a shaky start to the season, but Gary Hill of 710 ESPN points out Seattle has been just about untouchable since June 1.

ERA can be misleading at times, particularly for relievers, but the Mariners’ bullpen ranks first in the AL in FIP, xFIP and opponent’s average. A bit of regression is to be expected (and there has been some over the past week), but there’s no denying the group has put together a historic season.

So how did a terrible Seattle bullpen in 2013 rise so far in just one season?

Through a combination of drafting and previous deadline deals as sellers, the Mariners have amassed a collection of relievers who throw hard. Every member of the bullpen with the exception of lefties Joe Beimel and Charlie Furbush regularly touches the mid-90s or above.

Whether that’s something the organization specifically focuses on with relievers or if it’s just a reflection of a trend around the league, it’s contributed to the Mariners’ dominance.

Pitchers certainly don’t have to throw hard to be successful, but those who can hit the high-90s typically have more upside and strikeout potential. That’s reflected in the strikeout rate of 24.2 percent put up by Seattle’s bullpen, second in the AL to the New York Yankees.

With that much upside, the Mariners’ bullpen can go on some pretty incredible runs when everybody is clicking. Announcer Aaron Goldsmith highlights such a run earlier in August:

Some offseason additions and tweaks early in the season set the Mariners up well for their historic run. The team made two bullpen moves before spring training, adding veterans Beimel and Fernando Rodney to a relatively young group.

As frustrating as Rodney can be, he’s successfully solidified what was a shaky closer position in 2013. Locking down the back end has helped everything else slide into place, as manager Lloyd McClendon explained to Greg Johns of MLB.com.

“Everybody else was able to be slotted into the proper roles where they weren’t overexposed or overused. As a result, they’ve been fantastic. Now did I think they were going to be this good? This is historical type of stuff and I didn’t expect that. It’s been pretty special to watch.”    

The first big in-season move was to finally jettison Hector Noesi on April 3 and call up rookie Dominic Leone straight from Double-A. That left the Mariners without a typical long-relief or mop-up man, but they haven’t really needed one since the end of April.

Leone had far more upside and has rewarded the team for the decision. The 22-year-old has a 2.65 ERA (3.22 FIP) and is fifth among AL rookie relievers in strikeout rate.

The Seattle bullpen was already performing superbly by late June, but transitioning Brandon Maurer from the bullpen added another weapon to get the job done in any situation. Maurer looks like a completely different pitcher coming out of the bullpen and has allowed just five runs in 23.2 innings of relief.

A big factor in Seattle’s run has been that some of the returning faces have pitched to their full potential. In particular, Tom Wilhelmsen and Danny Farquhar have thrived in new roles after struggling to different degrees as closers in 2013.

Wilhelmsen has arguably been the most important member of the bullpen, as his versatility has provided tremendous value for the Mariners. He can be counted on in a critical late-game situation but has also been successful in longer outings of three or more innings and even made a spot start on July 10.

The key for Wilhelmsen has always been commanding his curveball, and he’s had a good feel for the pitch all season long. Wilhelmsen’s walks are down and his strikeouts are up, helping his ERA tumble nearly two points to 2.15 (3.73 FIP) in 2014.

Farquhar’s 1.86 FIP and 34.7 percent strikeout rate indicate he was unfortunate to have an ERA over four a year ago and his mark of 2.68 (2.43 FIP) in 2014 is far closer to his true talent level. FanGraphs indicated Farquhar is throwing his devastating cutter more often this season and is again striking out over 10 batters per nine innings.

Yoervis Medina has also improved his command from a year ago while shoring up some inconsistencies. Like Wilhelmsen, Medina’s been able to control his breaking pitches for much of the year and has decreased both his walk rate and ERA.

The member of the current bullpen who has struggled the most this season is Furbush, which seems like it would hurt the Mariners a lot more as he is one of only two left-handers available. However, Beimel (1.19 ERA, 3.35 FIP) has unexpectedly been able to pick up the slack, and Furbush has the fewest innings of any reliever (apart from Maurer) as a result. 

Credit must also go to McClendon for doing an outstanding job of managing the group. Fluid roles past the closer and an avoidance of overmanaging have helped the bullpen thrive.  

Finally, the Mariners’ strong starting rotation has helped the bullpen be successful. Seattle has tossed the third-fewest relief innings in the AL, keeping everyone available daily and fresh for the stretch run.

Seattle relievers don’t walk many (15.7 K-BB percentage, second in AL) and don’t allow many home runs (0.52 HR/9, first in AL). Those two numbers might be the most important indicators of success for a bullpen, so it’s not surprising to see the Mariners near the top in ERA.

The result is that McClendon can turn to a number of rested options who have proven themselves capable of shutting down the opponent in any situation. Beimel talked about the importance of such depth, via Johns of MLB.com.

“I’ve never been a part of a bullpen like this. Every single guy out there can get the job done, and that’s just fun to watch.”

A combination of potential, managing, a strong rotation and luck has helped Seattle relievers put up historic numbers. The Mariners’ rotation makes them dangerous in a potential postseason appearance, but a historic bullpen could be a huge factor in taking them there.

All stats via FanGraphs.com unless otherwise noted.

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