To begin the season, Brian Matusz sucked. Like, more-walks-than-strikeouts sucked. More precisely: From his 2015 debut on April 8th, to his May 19th outing, Matusz compiled 13.1 innings, in which he struck out 12.3% of the batters he faced, walked 15.8%, and gave up a 53.8% fly ball rate. A .184 BABIP kept his ERA at a low 2.70, but the 6.47 xFIP (!) he posted foreshadowed bad times to come.
Well, those bad times haven't come yet, and based on what Matusz has done since then, I'd say they won't come back this season. From May 21st until now, he's pitched about the same amount of innings as he did before, but to much better results: a 37.1% K%, 11.3% BB%, and 44.8% FB%, giving him a 3.07 xFIP for that span. Maintaining that depreciated BABIP, he's also allowed far fewer earned runs — 1.88 of them per nine innings.
Interestingly, Matusz underwent something of a similar transformation last year, when his 5.05 xFIP through the first three months of the year gave way to a 2.75 xFIP across the final three. Writing during that September, I observed the two impetuses of this: Matusz faced more lefties, and gained velocity. Those factors have helped to cause his 2015 reversal as well, but there's something else at play here.
As a starter, as a reliever, as a swingman, in a box, with a fox, Matusz has severely struggled against right-handed batters. They've abused him for a .365 wOBA this year, and for a .372 wOBA in his career. Lefties, on the other hand (get it?), have given him little trouble — he's held them to a 2015 wOBA of .214, and an all-time wOBA of .268. Thus, it makes sense that he'd do better when able to see more of the latter:
The Orioles, it seems, have deployed Matusz more intelligently, and have reaped the rewards of that decision. Of course, him throwing harder hasn't hurt — on every pitch in his arsenal, Matusz's velocity has spiked:
But handedness and power alone can't account for all of Matusz's improvement. Possibly the biggest change he's made comes from one pitch, which many people once deemed his best: his changeup. As a scrub, Matusz relied on it heavily; as a star, not so much:
The slider and four-seam fastball have all but phased out the changeup.
Why has Matusz relegated this formerly-deadly pitch to part-time duty? It certainly doesn't lack bite, as it took on more velocity than any other pitch in his repertoire, save the curveball. And while he toiled through April and most of May, it led all of his pitches in whiff rate (14.6%).
In terms of true talent, though, Matusz's slider and four-seamer most likely dwarf the changeup. The former two put up swinging strike rates of 16.5% and 11.0%, respectively, over Matusz's first two full years in relief (2013-2014), compared to 10.0% for the latter in that time. And indeed, since he turned the corner this year, the slider has induced 20.5% whiffs, the four-seamer 17.2%, and the changeup 8.0%. Recognizing this, and adjusting his usage accordingly, has driven Matusz to excellence.
Matusz's streak of progress is but one of the intriguing facets of this season for the O's, and we'll look at some more in the future. The halfway point of the 2015 season has just passed, so we still have a lot more baseball to go. Hopefully, Matusz will remain effective for all of that time; perhaps his teammates will follow his example, and make leaps of their own.