Simon Mercedes, RHP
With the exception of one start, May has been very kind to Simon Mercedes. He's posted an ERA of 3.00 on the month, with 23 strikeouts against 12 walks in his 24 innings of work. He's only allowed the one home run, and has managed to induce far more grounders than fly balls once again. It might not mean much of anything, but he's been better in his appearances where he's started rather than relieved: that could just be due to random happenstance, as four of his five starts have come in a row in May, or he could be far more comfortable coming in at the start of a game at this stage of his career.
At the least, it's worth paying attention to, since Mercedes is an arm that profiles as a reliever at the moment. Let's not make too much of a handful of starts against relief appearances that came after a promotion from short-season ball to High-A, though. For now, let's enjoy that Mercedes seems to be one of the few lower level arms with potential who seems to be putting things together effectively this month. He still has a long way to go and plenty of polishing to come, but this is a more impressive run than when he was 21 and beating down short-season bats.
Justin Haley, RHP
Haley probably doesn't need to be at High-A Salem any longer. He's managed to shed the walks that plagued him last year without sacrificing strikeouts, and has been as dominant in May as he was in April when he was first introduced to Carolina League competition. Whatever he has to learn next might not be taught until he reaches Double-A Portland. With that being said, promoting Haley isn't high on the priority list right now, mostly because it's hard to fit him anywhere besides where he is.
Portland currently houses Henry Owens and Brian Johnson, two starting pitching prospects who aren't going anywhere just yet, and wouldn't be bumped for Haley. Mickey Pena and Keith Couch are also in the Double-A rotation, as is the rehabbing knuckler Steven Wright, who doesn't have a spot in the Triple-A rotation at the moment. Mike Augliera is still making starts, too: that's three future relievers and a rehabbing pitcher all in one place, in addition to the two starting prospects. Haley is closer to the Pena/Couch crowd than to Johnson and Owens, so until a spot opens up, or the Sox decided that one of the Double-A future relievers is now a present-day reliever, Haley will probably stick in Salem.
Austin Maddox, RHP
May has been a disaster for Maddox, but mostly because of a pair of appearances in which he totaled seven runs allowed in 2-2/3 innings of work. Otherwise, on the year, he owns a 3.15 ERA, as he's only allowed 14 runs for the entire season. You can't just erase those awful outings, of course, but if Maddox goes on a run for a bit where he's doing well, it'll be hidden by this speed bump.
Overall, Maddox is having a solid bounce back season after a rough 2013. He's struck out 22 batters in his 21-2/3 innings, and done so against just three walks. The five homers are worrisome, especially since he gave one up in four consecutive outings, but that's fixable: we already know he can throw strikes, now he just needs to start throwing quality strikes. He won't see Double-A until he shows he's capable of mastering that important distinction.