What to Expect from Jonathan Aro

With Joe Kelly heading to Pawtucket and Justin Masterson being sent back to the rotation, the Boston Red Sox were in need of a bullpen arm. The bullpen so far this year hasn’t been the greatest and could use some youth. Justin Gorman lets us know what to expect from Jonathan Aro.

Ahead of their June 25th afternoon tilt against the Baltimore Orioles, the Boston Red Sox called up right-handed relief pitcher Jonathan Aro from AAA Pawtucket. This, along with recalling Deven Marrero and Jackie Bradley Jr. were part of a slew of roster moves, including Dustin Pedroia being sent to the DL, Joe Kelly being demoted to Pawtucket and Justin Masterson being placed back in the starting rotation to take Kelly’s start on Sunday. What can we expect from Jonathan Aro as he makes his major league debut?

The Red Sox signed Aro, a native of the Dominican Republic, as a non-drafted free agent on June 6, 2011, and immediately sent him to the DSL, where he put up very good numbers in limited action at a low level. Aro’s DSL stint spanned 47 innings, allowing 41 hits and issuing only four walks (though hitting six batters) on his way to a 3.06 ERA and 0.957 WHIP:

Over the next three years, Aro quickly worked his way through the Sox minor league system. After a disappointing season in the Gulf Coast League in 2012, the Red Sox organization decided Aro would be best used out of the bullpen, and that strategy paid dividends. His 2013 season with Lowell, as well as his 2014 season (split between Class A Greenville and High-A Salem) showed a sudden rebound in his numbers. In 2013, he threw 54 2/3 innings, striking out 49 while only walking 12 – good for a 2.14 ERA and 1.024 WHIP. While he issued more walks than in his 2011 DSL short year, he hit only two batters.

Aro’s control improved in 2014 – in 87 total innings (mostly in relief, though he did start one game for Salem) he struck out 98, walked 29 and hit only three batters. He averaged an impressive 10.1 strikeouts per nine innings, with a 2.17 ERA and 1.069 WHIP, and an opponents’ batting average of .189.

While those numbers are tantalizing, Aro’s rise through the Red Sox minor league system continued in 2015, where he started the season at AA Portland. After pitching 22 1/3 innings in southern Maine and putting up solid numbers, (2.82 ERA, 1.030 WHIP, 7.7 K/9), Aro ascended once again to the AAA Pawtucket Red Sox:

At Pawtucket, Aro pitched like a man possessed – in 10 relief appearances, over 22 1/3 innings, he notched a 1.61 ERA, 0.806 WHIP, and struck out 30, good for a 12.1 K/9 rate. It will be interesting to see what Aro contributes at the major league level – as it seems that with every rung of the ladder he has climbed in the minor leagues, his control has increased.

According to soxprospects.com, Aro’s arsenal consists of three pitches – including an average fastball that usually sits in the low- to mid-90s and an average changeup that creeps up to the plate in the low-80s. However, his best offering is a mid-80s slider which Aro is “confident throwing… in any count.”

In addition to harnessing his control, Aro’s spray chart is equally impressive. Keeping in mind that he has struck out 35.7% of the batters he’s faced at AAA, his pitches have stayed in the yard, as he has not allowed a home run. Aro is holding batters to a .188 average, with only a .300 BABIP, while keeping hitters noticeably off-balance. A quick look at his left/right splits show that of the base hits Aro has given up at AAA, the vast majority have been to the opposite field, regardless of the batter’s handedness.

It may be worth watching Aro’s velocity at the big league level – while the scouting report lists him at 6’1” and 175 lbs, recent video shows that he’s filled out his frame a bit more. As a result, he may have gained a few mph on his fastball, helping explain his dominance at AAA. Aro made his debut out of the bullpen for the Sox on the same day he was called up, giving up a run on four hits and striking out two in an inning and a third.

With the wealth of relief pitching prospects with near-household names still milling about in the minors (such as Steven Wright, Matt Barnes, Dalier Hinojosa, and Pat Light), the call-up of a relative unknown in Jonathan Aro was a bit of a surprise. However, with so many injuries and the Sox struggling mightily in nearly every aspect of the game lately, a positive performance by Aro (however small the sample size) may provide Sox fans with some comfort for the reasonably near future.

Follow Justin on Twitter @j1gorman.

About Justin Gorman 32 Articles
A native of New Hampshire, Justin grew up in western Massachusetts and is primarily a Red Sox fan, and secondarily an attorney. He and his wife live in the Atlanta area with their dogs. Justin is a co-host for SoSHCast (the Sons of Sam Horn Podcast) with Damian Dydyn.

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