Andrew Heaney – Heaney debuted in the Majors last year for the Marlins, but he struggled in his 29.1 innings, allowing six home runs. So he was traded twice this offseason and ended up an Angel after being dealt to the Dodgers from Miami. Heaney’s 4.71 ERA in Triple-A this year looks bad, but he had some bad luck due to a high BABIP and low left-on-base rate. His FIP was a nice 3.06. He’s pitched well in his two starts for the Angels, going 13 innings with 12 strikeouts and only two unintentional walks.

Last year, Heaney gave up all six of his home runs and 10 of the 12 extra-base hits he allowed on his sinker. This year, Heaney hasn’t changed his pitch mix, as he’s still throwing the sinker right around 65 percent of the time. But he is throwing it a lot harder, up from 91.16 to 92.37. It looks like the improved velocity has improved the pitch overall. Heaney’s made seven starts and nine total appearances in his short career, and his two 2015 starts have seen the highest whiff-per-swing rates (percentages) recorded on his sinker:

It’s not even close. His highest percentage of whiffs-per-swing last year on his sinker was 12, and this year he’s more than doubled that rate in both games. Heaney’s other two pitches are insane. He’s yet to allow an extra-base hit on his changeup in his career, and his curveball has a 47 percent strikeout rate on it. If Heaney can keep his velocity up on his sinker, I think we’ll see why MLB.com still ranked him the 25th overall prospect this offseason.

Steven Matz – Matz made his MLB debut Sunday against Cincinnati and pitched about as well as you could expect him to. The 24-year-old went 7.2 innings and allowed only two earned runs on two solo shots. He struck out six while walking three. Matz was really good in the minors at limiting home runs, and he was pretty good at limiting his walks, so I don’t think those events in his first start are indicative of how he’ll pitch from here on out.

According to Minor League Central Matz had a minor-league ground ball rate just under 50 percent, so I wouldn’t be scared off by his 33 percent rate after his first start. He throws three pitches – fastball, curve, change – and after watching his start it looked like his changeup was his best pitch, and the stats back that up. According to Brooks Baseball, hitters swung at 53 percent of Matz’s changeups (8/15) and missed on three swings, which is good for a 37.5 percent whiff/swing rate. That number was Matz’s best on the day out of his three pitches. I like Matz’s offspeed offerings, and I think he has some good potential to due well this year. But I don’t think he’s a necessary add in any leagues that aren’t at least 14 teams.

Mike Montgomery – The 26-year-old Seattle lefty was a fixture among top prospect lists between 2010 and 2012, coming in as high as 19 on Baseball America’s top 100 before the 2011 season. He was sent to Tampa Bay in 2012 as a part of the Wil Myers deal, but then really struggled in 2013-’14 and was sent to Seattle for Erasmo Ramirez on March 31. But once Montgomery finally debuted in the Majors he’s had a bunch of success. He’s pitched at least six innings in each of his six starts, notching five quality starts. He has a 1.62 ERA and 0.90 WHIP. He’s tallied back-to-back shutouts.

But when you dig a little deeper you see the success isn’t likely to continue. I want to start with his 83.7 percent left on base rate, which is 10 percentage points higher than league average. In his first shutout against Kansas City Montgomery loaded the bases with no outs in the first. He struck out Eric Hosmer and then induced a double play from Kendrys Morales. In the next inning he gave up hits to the first two hitters then struck out the side. You might think that he’s pitching well under pressure, and that may be the case. But all it take is one hit in those situations to get rid of the shutout and you’re not hearing about him on Baseball Tonight or MLB Network. He’s also benefiting from a .213 average on balls in play, well below the .295 Major-league average.

Another factor that’s helped Montgomery is his schedule. The Royals rank 18th in wRC+ against lefties and his next victim – San Diego – ranks 22nd in wRC+. Those two teams also rank 26th and 23rd, respectively, in Isolated Power against lefties. That could help explain his 2.3 percent HR/FB rate, and you should see that go up soon especially considering a not-special 44 percent ground ball rate. It’s good for the Mariners that Montgomery has pitched well in a down season for the club, but I’m skeptical that he’ll keep it up.