Ariel Pena Stumbling to Success in Brewers’ Rotation


Ariel Pena made his third turn through the Milwaukee Brewers’ starting rotation on Sunday, pitching five innings of two run ball against the Cincinnati Reds and collecting his second major league victory. When looking at Pena’s brief major league career, it’s fair to assume he’s off to a successful start: he’s 2-0 in four games (three starts), having pitched to a solid 3.50 ERA through his first 18.0 career big league innings. It’s long been believed that Pena would be more of an asset as a reliever than in the rotation, so has the righty’s strong debut started to dispel the notion that he can’t be successful starter in the big leagues?

It’s a small sample size, but looking a little deeper into Pena’s numbers will raise some concerns. Pena is still missing bats at a 20.5% strikeout rate in the major leagues, but that mark would be his lowest in a full season since 2012. He has allowed 11 free passes through his first 18.0 innings, or 14.1% of the batters that he has faced. He showed a little improvement in his control in the minor leagues this year, but so far has not carried this over to the big leagues. Pena has kept his WHIP to a 1.33 mark by allowing just 6.5 H/9 so far, thanks in large part to a low .245 BABIP. Ariel’s career BABIP against in the minors is much higher and he has allowed a hard hit rate of 38% this year, however, so there’s been some good fortune in those batted balls finding defenders’ gloves. He’s allowed just one home run and is boasting a 4.8% FB/HR ratio, numbers he hasn’t matched in the minor leagues. If a fly ball pitcher like Pena (42% fly ball, 38% ground ball so far) keeps giving up the same rate of hard contact, balls are going to start flying over the fence at a greater rate.

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Pitch counts have gotten the best of Pena so far, as well. With his lack of command just 42.8% of his pitches have been in the strike zone according to Pitch F/X, leading to some high pitch counts. Pena has thrown between 85-100 pitches in each of his three starts, yet has never gone deeper than five innings.

There’s also the question of pitch selection. Pena has been known as a fastball/slider specialist with a changeup that lacks quality as his third pitch. That report has been on point so far, as Pena has thrown 327 major league pitches so far according to Brooks Baseball: 204 four seam fastballs (62.4%), 108 sliders (33%), and just 15 changeups (4.59%). He’s recorded just two outs via the change, has walked a batter on it an allowed a single. Ariel’s been more low to mid 90s with his fastball (avg 92.48 MPH) than he has the “flamethrower” that’s been previously advertised. His changeup has averaged 87.14 MPH, giving it just a 5 MPH difference from the fastball where an 8-10 MPH velocity drop from fastball to changeup is more desirable. Pena also has demonstrated a much lower release point on his changeup than he does his fastball, so hitters can more easily discern whether he is coming with the heat or off-speed.

Ariel Pena’s vertical release point chart, courtesy of Brooks Baseball.

After starting the season in the Sky Sox bullpen, Ariel Pena was inserted back into the rotation and parlayed a solid seven start stretch into a big league call-up. He’s limited runs at the MLB level since replacing Matt Garza in the Brewers’ starting five, but he hasn’t done it it in a manner that lends itself to sustained success. Pena’s poor command leads to too many walks and high pitch counts, his changeup doesn’t differentiate itself enough from his fastball, and his BABIP and home run rate are due for some regression. FIP and DRA both say Pena’s ERA should be more than a half a run higher, and a 106 cFIP predicts a below average pitcher going forward. It’s nice to see the final piece of the Greinke trade experiencing some modest success in the major leagues, but one would be fooling themselves if they believe Ariel Pena is anything more than a reliever over the long-term.

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