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MLB Rookie Report: Peter O'Brien, 1B-OF-C, Arizona Diamondbacks

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The Arizona Diamondbacks promoted Peter O'Brien to the major league roster yesterday; he got one at-bat against the San Diego Padres, striking out. O'Brien is a somewhat enigmatic prospect with a combination of great strengths and significant weaknesses. Let's take a look.

O'Brien was originally drafted by the New York Yankees in the second round in 2012 from the University of Miami-Florida. He quickly impressed with his enormous power, hitting 22 homers in 2013 then 34 more in 2014, but had problems with contact and defense. He was traded to the Diamondbacks for Martin Prado in July 2014, then hit .284/.332/.551 with 26 homers, 31 walks, and 124 strikeouts last year in Triple-A. He got a cup-of-coffee in the majors and went 4-for-10 with a homer and five strikeouts.

From the 2016 Baseball Prospect Book

Peter O’Brien, C-1B-OF, Arizona Diamondbacks
Bats: R Throws: R HT: 6-5 WT: 225 DOB: July 15, 1990

2014: Grade C+; 2015: Grade C+

No mysteries with Peter O’Brien’s bat: he can mash. Make a mistake and this guy will hit it to Saskatchewan. However, the danger is containable if you coax him into chasing something outside the strike zone, which he is wont to do, or if you can get up and inside where his long swing can’t get around well. Still, any location mistake and you’ll pay. This is 20+ homer power in 500 big league at-bats, but he might have trouble hitting .240 and he’ll strike out a lot. If O’Brien could catch he’d be a fine regular but his defense behind the plate has never really panned out. He tries hard and he has a good arm, but he struggles with receiving and making accurate throws. He spent most of last year in the outfield with weak results but has been adequate in brief trials at first base. It seems something of a waste to leave power of this quality trapped in Triple-A but without much better defense it is hard to see where he fits, at least for a National League team. Grade C+.


O'Brien continued his mix of power and shaky discipline this year before his promotion, hitting .306/.330/.601 for Reno with just six walks and 54 strikeouts in 173 at-bats. He hasn't caught any games this year, splitting his time between left field and first base. He's developed into a pretty good gloveman at first base but remains mediocre in the outfield. At this point his skills behind the plate are best used in the third catcher/emergency role.

The pre-season take is still my opinion: this guy will hit homers but don't expect him to draw walks or hit much higher than .250 if he gets to play regularly. Despite his weaknesses, his power could be quite useful as a role player for many teams.