I figured I'd try something a little more objective here. So, I pulled the data on the relievers who had appeared during most games in the minors this year, regardless of level. I filtered this to remove players with major-league experience [Matt Reynolds and Enrique Burgos being the most obvious], those who threw a total of less than 15 innings, and also anyone in their age 27 season or older, who are likely to be roster filler. This gives us a list of 20 players, shown in the following table, along with their stats, combined across levels where necessary. Left-handers are marked with a *, and all stats are through June 4.
I'm not going to detail all of these, because in most cases, I'd be simply going off the numbers here. But I do want to highlight a few of these. Let's start with Zac Curtis, currently leading in the chase for the 'Enrique Burgos I'm gonna strike everyone out Cup": sixty outs recorded, thirty-four of them by the whiff. He's not the only relief prospect to be getting more than half his outs with strikeouts, but his K:BB ratio of 34:5 is the most impressive. We should also mention Joey Krehbiel (70 outs, 37 K), who is the same age is Curtis, but a level higher. Nick Sarianides (61 outs, 32 K) is there too, but he turns 26 in August and, frankly, shouldn't be in High-A at that age.
Probably the best overall performance belongs to Silvino Bracho, Having destroyed A-ball pitching last year (70 strikeouts in 43.1) innings, he was promoted to High-A to start 2015. This presented only a light challenge: after six innings of one-hit ball, with fourteen strikeouts, he was moved up to Double-A, where the 22-year-old has been hardly more challenged: one earned run in 11.1 innings, with 12 strikeouts and two walks. That shining 26:3 K:BB ratio is stellar, and in sharp contrast to Burgos's age 22 season, where his ratio was 50:49. If he can keep this up, Bracho has "future closer" written all over him.
He doesn't however, have the best ERA. That belongs to leftie Keith Hessler, who took a little longer - four more appearances - at Visalia, before getting the call, though actually made his debut with Mobile before Bracho. He had 14.2 scoreless innings for the Rawhide, and extended the streak by four innings with the BayBears, before allowing his first - and, to date, only - run. Against this, he is 26, and his track record might lead one to wonder if this is some kind of statistical fluke, since Hessler's ERA over 45 appearances last season was a pedestrian 4.33. The rest of the year will show whether this is a break-out or an aberration.
At Triple-A, you wonder what Kevin Munson has to do, to merit a call-up to the bigs, especially considering how badly the bullpen has been struggling It's no small-sample size fluke: since the beginning of 2014, he has thrown 79.1 innings for Reno, in a very hitter-friendly league, and had an ERA of 2.27. Considering Dominic Leone last night became the twenty-fifth different reliever used by the D-backs over that time, including such memorable names as Bradin Hagens and Bo Schultz... It'd be funny if we activated Munson for the Phillies series in August: like Ender Inciarte, Munson was picked in the Rule 5 draft by Philadelphia, but was subsequently returned to us.
Alongside Munson in Reno is another name about which there has been chatter: Jake Barrett. However, he seems to have hit a bit of a road-bump lately. After his first 15 appearances, his 1.69 ERA and 19 strikeouts over 16 innings looked pretty good. Since then though, he has allowed eight earned runs over his last six games and innings. A BABIP of .444 likely plays into the 13 hits allowed by Barrett; on the other hand, allowing more walks than strikeouts (K:BB 2:3), is entirely on Jake. With David Herhandez just about due to return, the current window of opportunity may be closing somewhat for Barrett.
Finally, one who hasn't been as impressive as hoped, Jimmie Sherfy, who was at #9 in John B's top 10 back in November, with the note that he had overcome a bump in the road - his Arizona Fall League performance had been great, allowing one run in 9.2 innings, on five hits and three walks, with 10 strikeouts. Unfortunately, his second stab at Double-A does not seem to have gone much better than his first, with an ERA of 4.22, that's not much improved on the 4.97 figure last year. Youth is still on his side, as he won't turn 24 until December. However. that will not remain the case indefinitely, and with the likes of Bracho behind him, Sherfy needs to keep improving.