Oakland A's relievers by the numbers: Ryan Madson has cleaned up the 9th inning

Rich Hill pitched on Monday, which means we won't have good news about the starting rotation again until this weekend when he goes again. Instead, let's take a look at the bullpen. Here's one key stat for each of the eight relievers currently on the 25-man roster, one of whom will go down on Wednesday to make room for spot starter Zach Neal. As a whole, the relief corps ranks middle-of-the-pack in MLB in the big-picture stats, but they're among 11 teams that have blown only four saves or fewer. They are listed here from the best ERA to the worst.

Ryan Madson, RHP | 92.3%

That's his conversion rate, in terms of entering with the lead and converting it into a save or a hold. He's been in 13 save situations, with 11 saves, 1 hold, and 1 blown save. His ERA is low, even though his Ks are down and his walks are up, but last year we learned how little a good stat line matters if you always collapse at the worst time. Madson is the closer now and the bottom line is what he does with the leads he is given. So far he has been nearly perfect in that regard.

Fernando Rodriguez, RHP | 24⅓

That's the number of innings he's thrown, tops in the bullpen. He's done that in 17 appearances, with 11 of them lasting more than three outs and four outings of at least two full frames. Rodriguez has teamed up with Ryan Dull to give the A's a pair of quality workhorses in the pen, which has been crucial given the failure of the starting rotation so far. For his part, Fernando is striking out a batter per inning while severely limiting the hits and homers, so he's making good use of those innings as well.

John Axford, RHP | 95.4

That's his average fastball velocity according to FanGraphs, the hardest of all A's relievers by more than a full mph. If you prefer Brooks Baseball, they have Axford at 96.3 mph on average, still a full tick better than anyone else. The runner-up via both sources is Doolittle, at 94.3 (FanG) or 95.1 (Brooks). Brooks also has Madson and Hendriks at 95 mph on average. The point is that this group throw hard, with Ax leading the charge in that department. His velocity ranks 23rd among 175 qualified MLB relievers.

Sean Doolittle, LHP | 90.16%

That's how often he threw his four-seam fastball in the month of May. Doo struggled in April, allowing four walks and three homers in 13 games, and Brooks suggests he was trying out a splitter during that time with only 83% four-seamers. In May he's gone back to relying almost exclusively on his fastball, with a few sliders mixed in, and he's looking like his old self again: 12 Ks, 2 BB, and no homers in nine games. I must stress that this is a correlation and we can't be sure of the cause -- perhaps he needed that first month to shake off the rust of missing most of 2015, and the pitch selection aspect is a pure coincidence. But he did something different in April and got hammered, and now he's back to his old style and enjoying his old success. Consider this something to keep an eye on.

Ryan Dull, RHP | 5.00

That's his strikeout-to-walk rate, the best on the team. Dull was the last reliever to make the Opening Day roster, but he has proved himself already. He's been one of the go-to guys in tough middle-inning situations, and like Rodriguez he's shown he can throw multiple frames (five outings of at least five outs). He's not unhittable, as evidenced by his 4 homers in 23⅓ innings, but he's efficient and he keeps the damage to a minimum when he does get in trouble.

Marc Rzepczynski, LHP | 78.3%

That's his ground ball rate, which is second in all of baseball behind well-established grounder expert Zach Britton (78.4%). For context, only seven qualified relievers are even above 70%, and only 17 are above 60%. Zep has always kept the ball on the ground thanks to an arsenal that relies primarily on a sinker, but for the second straight year he's setting a significant career high. Could this have anything to do with the fact that he's added a changeup? Brooks says he's going offspeed 17.7% of the time, far more than he ever has before, and it's coming at the expense of his slider. That's odd, since his slider used to be his best offering, but he's not the only A's hurler to back off from that particular pitch this year and it seems to be working so far.

Andrew Triggs, RHP | 19.4%

That's the percentage of the time opponents have made hard contact, according to FanGraphs. This doesn't mean much in such a small sample (11 innings), but for now that number is lower than any of the six guys above so at least Triggs is off to a good start. Like Zep, he keeps the ball on the ground most of the time (67.7%), as you might expect from a sidewinder, and weak contact plus ground balls is a wonderful combination. He's already been worth the waiver claim it took to get him, and if this turns out to be the real Triggs then we'll end up looking at him as an outright steal.

Daniel Coulombe, LHP | 0.56

That's his ERA ... in Triple-A. The lefty is last on this MLB list because he's only pitched for the A's twice and got smoked in an emergency mop-up outing in Boston, but he's been lights-out for a Nashville Sounds team that leads the Pacific Coast League in ERA by more than half a run. His peripherals in 16 MiLB innings are insane: 19 Ks, 3 BB, 7 hits. He's properly cast in his current role, as a taxi reliever who covers the middle innings when he's in Oakland, but you could do so, so, so, so much worse in terms of your bullpen depth.

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