The Evolution of Jace Peterson

The 2015 Braves aren’t supposed to be competing. Despite the insistence from the front office that this isn’t a rebuilding year, the number of young kids who were given roster spots at the beginning of the season told a different tale. There are a lot of reasons this team continues to linger around .500, ranging from sheer dumb luck, to Cameron Maybin’s break out after a career filled with injuries, to a renewed focus on defense. One of the biggest, however, has been the emergence of Jace Peterson as a legitimate offensive player at second base.

Acquired in the Justin Upton trade, most expected Jace Peterson to grab the starting second base job, at least long enough to bridge the gap to top ‘spect Jose Peraza. Peterson’s minor league profile indicated a good batting eye and a contact-oriented approach. He consistently posted walk percentages north of 10%, struck out less than 15% of the time, and posted BABiP’s around .330, without much power to speak of. This type of profile doesn’t generally translate to the majors well, as walks become harder to earn in the majors absent the threat of power, and without elite speed or an obscene hit tool, a .330 BABiP is tough to sustain. To quote Fangraphs’ Kiley McDaniel, who listed Peterson as a 40 FV prospect at the beginning of the season, “[Peterson] may not even have a 55 tool, but he makes the most out of what he has.”

Early in the season, it was evident Peterson was quite gifted with the glove, finally giving Andrelton Simmons a reprieve from covering everything from Freeman to third. But man, did he struggle with the bat. I’m not a tremendous fan of arbitrary endpoints, but following the Cincinnati series on May 3, Peterson’s OPS sat at an abysmal .580, with a wOBA under .250. He was also striking out 20.5% of the time, and managed only one extra-base hit—a triple—through the first 29 games of the year. He looked a lot like the same kid that struggled to get on base and make quality contact in his cup of coffee with the Padres last year. This represents something of a low water mark in what was a tumultuous beginning to Peterson’s Braves career. Then the rest of May happened.

Peterson took off, using May to get his rates back to a respectable level, and he’s carried his torrid pace into June. Since that low point on May 3, Peterson’s rocked a quality .306/.373/.431 line, cutting his K% to under 17%. This past week, he finally surpassed a 100 wRC+, breaking into positive batting value territory for the first time in his major league career. He’s done that by cranking out a .333/.407/.490 line since the calendar turned to June, and—small sample size aside—Jace finding a way to incorporate a bit of power into his game while maintaining a 10%+ walk rate and a healthy BABiP is great news for his future. Some of this is simply regression, but a couple of mechanical tweaks may also be responsible for Peterson cutting his K% and bringing more power to the plate.

We’re going to do a couple comparisons, working backwards from the Jace we’re all familiar with now. We’ll start with his at bat against Santiago Casilla when the Braves were out west last week.

jace 15

Jace Peterson, May 2015

This is the Jace we’ve seen for the better part of a month now. As you’ll see, he’s quite crouched, allowing him to have a still head in the batters box. His bat and hands are relatively quiet through load, and his slight leg kick is being used less as a timing mechanism, and more as a means of driving his lower body and his hips through the ball. This is a veritable meatball from Casilla, but we see great balance, weight shift, and rotation through the body.

Now, we compare that to Peterson last year, in San Diego.



Jace Peterson – 2014


Here’s Peterson’s first major league hit against a fading Stephen Strasburg change up (PitchF/X classified it as a fastball but check ya boy’s grip). There’s a few things of immediate note: he’s very upright, hitting against a much narrower base than he is today. Because he’s so upright, he’s got to change eye level pretty significantly once he’s in hitting position, and from release to contact, his head drops about 8 inches, making it much more difficult to find consistent contact. His hands are exceptionally noisy, which isn’t an issue unto itself, but despite facing a change up here (albeit a 93 MPH change up), Jace’s hands never really load to the extent that they do in the first GIF. Furthermore, Peterson’s leg kick takes him over the plate to cover the outside corner, but unlike 2015, he’s not driving through the ball, and I found much more video of him locking his hips out and preventing full rotation–as he does here–than I found from 2014 and the minors where he was able to maximize rotation.


Jace Peterson, April 2015

This brings us to April 2015, as Jace started out his Braves career. We see some pretty significant changes already, and perhaps an off-season of work with Kevin Seitzer brought about some of these tweaks, and his work after April is merely the fruits of that labor. He’s still much more upright in April than he is even a month and half later, and the result is his head dipping, but only 4 inches or so, and all before the pitcher releases the ball. He’s essentially in the same positions at load and trigger as he is today. He’s still got a bit more hand movement compared to today, but it’s slower, calmer, and he’s now able to get his hands loaded as he gets into hitting position. We also see him hitting off a wider base, letting him open up his hips and rotate on the ball against the grain of a leg kick that closes his body off.

Simple regression can speak for some of Jace’s turnaround, but we’re also looking at a wholesale change in his mechanics over the last calendar year. Minimizing head movement should help cut K% and potentially improve an already good eye as he gets a more consistent look at the ball out of the pitcher’s hand. Hitting against a wider base, getting his hands primed at load, and being able to utilize his lower body could potentially add the bit of power he’ll need to go from second division starter to a key contributor on the next Braves team that loses in the NLDS. With all the usual caveats that apply to a player this young and with this little of a track record: perhaps we’re already seeing some of that now, with Jace posting a .125 ISO since May. At 6’0″, 210, I could see him potentially topping out around Yunel Escobar territory, with a .120-.130 ISO. Given that Peterson hits more liners and fly balls than Escobar, both in his short major league career and in comparing scouting reports, it wouldn’t be too much of a surprise.

The difference is if Yunel isn’t hitting for power, he’s barely playable. Peterson brings a better batting eye to the table than Escobar ever showed, and he has the wheels to be an asset on the base paths and a weapon in the field. Those traits have been on full display, as Jace has accumulated 1.7 fWAR thus far despite an ISO that is still below .100 for the season. Extrapolated out to 650 PA’s, that’s over 4.5 wins. We don’t know enough to definitively say whether he’s a .330 BABiP guy, or if he’s a 10+ DRS defender at 2B. But even with regression in those areas, if he can turn these mechanical changes into at least playable game power on a long-term basis, then a few 3 win seasons, maybe a fluke 4+ win year or two (RIP 2012 Martin Prado), aren’t out of reach.

A.J. Preller 2016.


I loathe Nick Markakis

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2 comments on “The Evolution of Jace Peterson
  1. Steve-o says:

    Nice bit. I haven’t been paying close enough attention to notice his rise into respectability.

    One quibble: you shame your calculus professors by classifying a perfectly reasonable inflection point as a mere “arbitrary endpoint.”

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