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Oakland A’s prospect watch: Jonah Heim stepping up in High-A Stockton

The A’s thin catching ranks have a new name to follow.

Jonah Heim
Meghan Camino | Stockton Ports

The Oakland A’s have one of the best minor league systems in all of baseball, but one area where they are particularly thin is catching. At the MLB level they have short-term veteran Jonathan Lucroy on a one-year contract and Bruce Maxwell on the bench, and their Triple-A ranks are full of unexciting backups. Entering the season the only other notable name in full-season ball was Sean Murphy in Double-A, and after that you had to look all the way down to Low-A/Rookie Ball for someone like teenager Santis Sanchez.

A new hope has emerged at High-A Stockton, though. The A’s acquired Jonah Heim from the Rays last winter, in exchange for infielder Joey Wendle. The 22-year-old (23 in June) arrived with an excellent reputation behind the plate, including his defense, arm, game-calling, work ethic, and general makeup, which at the very least would make him quality org filler — after all, someone has to work with all the pitching prospects who come through town. However, he’s also beginning to hit enough that he could wind up on the legit prospect radar.

Heim: .317/.373/.460, 126 wRC+, 3 HR, 7.8% BB, 17.0% Ks

The switch-hitter was drafted out of high school, so he spent his first couple pro seasons in Rookie Ball. He struggled in High-A in 2016 but then found his first offensive success last year at Single-A (112 wRC+), and now he’s building on that in his return tour of High-A. His 2017 stats were nearly identical in terms of strong plate discipline, high contact rate, and midlevel power, but a bump in BABIP has his slash rates 40-50 points higher so far this year.

On Sunday, Heim posted an 0-fer at the plate, which snapped a 19-game hitting streak dating back to mid-April. During that streak he batted .410 and posted a 1.015 OPS, with nearly half of his batted balls falling for hits and 10 of his 24 hits going for extra bases. According to the A’s, it was the longest hitting streak for an Oakland minor leaguer since 2014.

There’s still the possibility of some small-sample shenanigans in Heim’s stats, so we shouldn’t take his breakout as gospel just yet. But that .369 BABIP isn’t so outrageous that we have to discount it out of hand, and there’s no reason to doubt his fundamental skills of contact, moderate power, and plus defense. At the very least, Heim is looking like a quality acquisition for a player (Wendle) who was on his way out the door anyway, and there’s the chance he could turn into an outright steal.

Rest of lineup

Not much new to report in the rest of Stockton’s lineup, but here are a few notes:

  • OF Skye Bolt is still showing there’s nothing left to prove in High-A, with a 166 wRC+, plenty of power (.261 isolated slugging), and a huge walk rate (17.2%). This is the best he’s ever played at any level, even in a small sample, so hopefully that means the 24-year-old will be ready for another chance at Double-A whenever the opportunity arises.
  • OF Dairon Blanco picked up six hits over his last two games, and over his last eight outings he’s 10-for-30 with a few walks. The 25-year-old still has a below-average line overall in his U.S. debut, but he’s gradually trending upward and he’s at least using his blazing speed along the way (9-for-10 on steals).
  • 2B Nate Mondou is heating up at the plate, going 11-for-24 over his last seven games. That’s good for a .458 average and 1.038 OPS, with more extra-base hits (3 doubles) than strikeouts (2). His wRC+ is up to 94 for the season, after a particularly slow start. His tiny strikeout rate (11.6%) is fueled by the lowest swinging-strike rate in the entire Cal League (5.2%).


Steady as she goes. Parker Dunshee and Brian Howard are still excellent, and Logan Shore is still pitching like a guy who would be in Double-A right now if he’d been healthy to start the year. Zack Erwin, Jake Bray, and Matt Milburn make up the tier below them. Here’s a stats update:

Shore 1.69 16 18 1 0 2.30
Dunshee 2.70 40 52 10 3 3.07
Erwin 4.13 32⅔ 26 11 1 3.98
Bray 2.36 26⅔ 18 12 0 4.02
Howard 3.08 38 41 9 5 4.14
Milburn 5.29 32⅓ 26 5 6 5.16

And the bullpen, where Boomer Biegalski, Angel Duno, and Miguel Romero are the standouts, alongside lefties Will Gilbert and Andrew Tomasovich. Of particular note, Romero has now faced 66 batters this year without walking any, while Biegalski has struck out 37.5% of his own batters.

Biegalski 3.26 19⅓ 30 5 2 2.82
Duno 1.88 24 27 5 2 3.26
Gilbert 0.00 11⅔ 9 4 0 3.28
Romero 1.93 18⅔ 19 0 2 3.32
Tomasovich 3.31 16⅓ 22 14 0 3.86

There’s another gaudy strikeout rate in right-hander Sam Sheehan (29 in 17 innings, 35.8% of batters), but the rest of his numbers are pretty ugly so he doesn’t quite make the list yet. His 3.62 FIP gets him a mention in this footnote.

Tuesday’s games

Full slate of action, with a double-dip in Beloit.

Triple-A Nashville: Won 7-4, Daniel Gossett vs. Memphis
Double-A Midland: 4:30 p.m., Norge Ruiz vs. Frisco
High-A Stockton: 7:10 p.m., Matt Milburn vs. Rancho Cucamonga
Single-A Beloit (1): Lost 4-2, Jared Poche’ vs. Wisconsin
Single-A Beloit (2): LIVE, Bryce Conley vs. Wisconsin

Another scoreless gem by Gossett. The other name to watch here is Ruiz.

Link to box scores