Craig Stammen. (Photo by Joe Sargent/Getty Images)

By many measures, the Nationals bullpen has been the best in baseball this season. There is one arm in the bullpen that, despite his stellar production, gets little attention, and that’s been the case for much of his career. Such is the nature of Craig Stammen’s jack-of-all-trades job. Middle relievers are rarely in the spotlight.

But Stammen’s versatility and importance was on display this past week. Last Tuesday against the Astros, the Nationals needed a bridge from Tanner Roark’s five-inning start to the back of the bullpen, and Stammen fired a scoreless sixth. On Thursday against Atlanta, Matt Williams needed a final inning in a loss, and Stammen delivered a scoreless ninth. Again, the Nationals needed some innings from a bullpen arm Friday trailing 4-2, and Stammen pitched a scoreless eighth and ninth, allowing Anthony Rendon to tie the game with a two-run shot off Craig Kimbrel.

On Sunday against Atlanta, Roark’s pitch count was high and had two runners on base with one out in the sixth, and Williams again called for the bulldog from the bullpen. Stammen escaped the sixth inning and added a scoreless seventh for good measure.

“That’s who I am,” Stammen said. “This week is probably the standard for that of being ready in any situation. I try to show up to the ball ready to play and ready to go. My biggest asset is being able to pitch every day and being multi-faceted. That’s what keeps me on the team.”

“He doesn’t take into account any inning in particular,” Williams added. “You give him the ball and he goes and pitches. And he pitches great. He pitches hard.”

Since 2012, no reliever has logged more innings (208 1/3) than Stammen. His 2.5 WAR (’s Wins Above Replacement), a significant contribution from a middle reliever, in that span leads all Nationals relievers, a hair ahead of Tyler Clippard’s 2.3 fWAR. His 2.55 ERA is 23rd in baseball, sandwiched among closers and set-up men. His ERA sits at 2.58 and, thanks to fewer walks, has a career-high 6.20 K/BB rate through 38 1/3 innings this season.

“He’s our workhorse,” Clippard said. “Craig can really do anything that you ask him to do. It goes with a lot of those guys down there, but Craig more importantly. The fact that he’s going multiple innings, he’s pitching in big situations, he’s coming in with the game on the line and runners on base. Every situation possible. There’s not too many guys in the league like him and he’s very valuable for us.”

Middle or multipurpose relievers like Stammen rarely make all-star teams, but the right-hander is in the midst of a stellar season for the third straight year. His ERA in 2012 was 2.34 over 88 1/3 innings. His ERA in 2013 was 2.76 over 81 2/3 innings. He has an ERA+ of 151 (meaning he is 51 percent better than the league average) in that span. Stammen and his rubber arm are a model of consistency. His ability to pitch in any inning, and stay healthy, gives the Nationals back-up options in every role.

“When guys are down or if I need a day, or Drew [Storen] needs a day, we always know we can rely on him to step into those roles and do the job as well as we can,” Clippard said. “It just takes pressure off of everybody, it makes everybody feel confident. The team, the coaching staff, everybody feels confident in putting those guys in those situations, especially Craig.”