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Contextualizing Renato Nunez

A's prospect Renato Nunez is slugging .500 in the Midwest League as a 19-year-old. However, he also has struck out almost five times as much as he's walked. What can we make of him by putting his accomplishments in a historical context?


Few Oakland prospects have raised their stock this year as much as Beloit third baseman Renato Nunez. The Venezuelan teenager has followed up on an impressive 2012 campaign in the Arizona League (.325/.403/.550) with a solid first half in the Low-A Midwest League (.281/.333/.500), a circuit known for being tough on hitters in the cold early months.

I don't live in an area that really is accessible to the Midwest League, so I can't vouch for what Nunez looks like in person. Instead, today I'm going to try to put his 2013 performance in perspective and see how comparable hitters have fared.

Let's start with what Nunez does well. He's already launched twelve home runs. He's slugging .500, with a .219 Isolated Power. In the last 25 years (1988-2012), only 41 19-year-olds sustained a .200 ISO or higher in Low-A. Only nine of them have never played in the majors, and four of those (Miguel Sano, Gary Sanchez, Matt Davidson, and Javier Baez) seem likely to reach the bigs at some point, with a fifth (Trevor Story) possible. A full half of the hitters made some sort of an extended big league impact--if Nunez is already at the point where he has a 50% chance of being a solid MLB hitter, that's a heck of a thing to say about a teenager.

On the flip side, though, Nunez has sixty-nine strikeouts and just fifteen walks this year. That strikeout rate of 27.9% would rank fifth-worst of the 41 (well, 42, including him) hitters, ahead of only notorious whiffmasters Wladimir Balentien, Wily Mo Pena, and Russell Branyan and the forgotten Glenn Williams. His 6.1% walk rate is thirteenth-worst, and his .22 walk-to-strikeout ratio only beats out those of Balentien, Pena, Josh Vitters, and Javier Baez.

Nunez is also fielding .873 at third base, which is an issue, though young third basemen often commit a lot of errors. Having not seen him personally, I'm not going to offer an opinion on his defense; today, I just want to focus on Nunez's offensive potential.

Clearly, we have two prominent numbers offensively to deal with here: Nunez's power output and his inability to control the strike zone. Naturally, when a prospect has such definitive strengths and weaknesses, some analysts will believe the strengths will ultimately win out in the end, while others believe the weak points will sink the player's career. Rather than subscribing to either of these viewpoints, I want to look at what a high strikeout rate and low walk rate mean for a player that shows such strong in-game power at this age, using the sample of the 41 .200+ ISO 19-year-olds.

First off, let's look at how the players tended to fare in their age-20 seasons (usually in High-A, though a few went to Double-A). Here's age-19 strikeout rate vs. age-20 strikeout rate:


And the corresponding walk rates:


Finally, the walk-to-strikeout ratios:


There are fairly high correlations on all three--not surprisingly, a hitter's strikeout rate, walk rate, and BB/K at age 19 tend to predict those same numbers at age 20. One thing that does jump out, though, is how few outliers there are to that trend. Only five of the forty-one managed to cut at least 5% off their strikeout rate from age 19 to age 20, and only four saw their K-rate increase by over 5%. Just about half the players were able to decrease their strikeout rates, and just about half were able to increase their walk rates. No batter in the group was able to increase his walk rate by more than 4.3% (Cliff Floyd), though five did lose at least 4.3% off their walk rates, with the worst being former Cubs prospect Jeff Goldbach (6.8%), one of the few who never made it to the big leagues.

As a result, it doesn't seem like K/BB breakthroughs or collapses are all that common, at least for prodigious sluggers. Over 3/4 of the hitters (31 of 41) saw their BB/K ratio change by .2 or less from 19 to 20. The two huge outliers are Goldbach (who lost 6.8% off his walk rate while seeing his K% go up 2.5%) and Rockies third baseman Nolan Arenado (who cut 3.9% off his K-rate while adding 3.3% to his walk rate).

So, if Nunez ends the 2013 season with rates near where he is now, it seems highly unlikely he will suddenly morph into a disciplined contact hitter in 2014--there's no precedent for that, really. Arenado was the only player in the sample who went from a "bad" BB/K (.37) to a "good" one (.89), and unlike Nunez, Arenado always had very low strikeout rates--he just refined his contact-heavy approach to include a few more walks as a 20-year-old.

At the same time, at least it doesn't seem like Nunez is guaranteed to go all Telvin Nash/Cody Johnson and suddenly start whiffing 40% of the time. Plugging his 27.9% strikeout rate and 6.1% walk rate into the formulas given my the regression equations on the charts, we get a projected 26.1% strikeout rate and a 7.4% walk rate for him next year, which would bring his BB/K from .22 to .28. Using the BB/K regression equation, he actually projects to move up to .32. So while dramatic improvements seem highly unlikely in the near term, a total dropoff also has few precedents (Goldbach and the early returns on Trevor Story's 2013 seem to be the sole strong cautionary tales).

The other interesting question regarding the age-20 performance is the maintaining of power. All the hitters showed tons of power at 19, but how many held it up against higher competition? Less than half (17 of 41) were able to maintain Isolated Power marks of .200 or higher, and thirteen actually fell to below .150. I wondered if the walks and strikeouts predicted the age-20 ISO in any way. BB/K ratio itself actually doesn't, which surprised me. The walks and strikeouts themselves, however, both showed small positive correlations, perhaps a sign that more selective hitters have an easier time maintaining their power than overaggressive ones. This makes intuitive sense, even if the fact that strikeouts have a positive correlation with ISO may take a second to get one's head around--as a batter moves up, he faces pitchers who are likely to make fewer mistakes, so an aggressive, contact-driven approach is likely to result in weak contact more than a patient one, even if the latter means lower contact rates in general.

Even then, though, the age-19 walk and strikeout rates don't predict the age-20 ISO in any way. The only significant correlation is between age-20 non-contact rate (walk rate + strikeout rate) and age-20 ISO:


If we really want to get hypothetical, we can plug Nunez's projected BB% of 7.4% and K% of 26.1%--a non-contact rate of 33.5%--into this formula and come up with a projected ISO of .204 for next year. I wouldn't take anything from that, but at least the (shaky) math we have doesn't damn our prized prospect.

From what we can tell from these charts, it seems the 2014 prognosis for Nunez is mildly optimistic. He may make a bit of progress with his plate discipline while continuing to show off his power stroke at age 20 in High-A; if he does as well as these formulas project him to, I won't be ecstatic, but I'll hardly be bemoaning his lack of progress as well. The fact that Nunez's plate discipline rates weren't all that bad in the AZL (9.1% BB%, 17.3% K%) last year does nothing to dispel the idea that some improvements could be on the horizon, though a look back to 2011 in the DSL reveals a problematic 2.9% walk rate and 20.3% K rate, so the track record is mixed even at the lowest levels of pro ball.

Of course, none of us are thinking about what Nunez might do in a Stockton Ports uniform; what we're most concerned with is what he might do in an Oakland A's jersey at some point. We've looked at how these players translate to their age-20 seasons, but how do they translate to the major leagues?

As I mentioned before, 32 of the 41 made it to the big leagues, but eleven of those players either did not or have yet to accumulate enough MLB plate appearances to establish any sort of "MLB true talent level" of performance. That leaves us with twenty-one to really compare career prognoses with.

However, one thing we can do is split the sample into two groups: players who "made it"--those 21--to significant MLB playing time, and those who definitely didn't (ten players; the other 11 are still "prospects" in some form). Does anything jump out as different with their age-19 and age-20 numbers?

Group Age-19 K% Age-19 BB% Age-19 BB/K Age-20 K% Age-20 BB% Age-20 BB/K Age-20 ISO ΔK% ΔBB% ΔBB/K
Successes 20.55% 8.3% .45 20.06% 8.97% .48 .198 -.5% +.7% +.03
Busts 22.12% 10.25% .5 22.44% 9.33% .45 .166 +.3% -.9% -.06

The successes do indeed grade out better, though mostly in terms of age-20 performance--they actually started out with a significantly lower walk rate and a lower strikeout-to-walk ratio. However, the group maintained their power through age 20 far better than the bust group did, and the successes marginally improved their plate discipline while the busts saw their zone control slide backward at age 20. It does seem, then, that the prospect's ability to quickly adjust to the next level at age 20 does portend some things about his future. All of the players in the sample who went on to post .340 or higher wOBAs in the majors either had an ISO above .200 at age 20 or improved their K/BB from 19 to 20. Kelly Johnson, Butch Huskey, Juan Encarnacion, and Javier Valentin were the only four players to do neither and go on to respectable MLB careers.

What about within those twenty-one players who went on to significant careers, though? Do the age-19 or age-20 performances carry significant weight as to how well they'll fare in the majors?

Both age-19 and age-20 strikeout rate carried immense weight on a batter's future MLB strikeout rate, with r2 values of .68 and .79--extremely high correlations. The r2s for walks were lower, at .42 and .41, but still showing a significant correlation. This shows that patience may be a more malleable trait than contact ability over time.

Still it seems that plate discipline is fairly static. None of the twenty-one hitters increased his walk rate by 5% or more from either age 19 or age 20 to the majors. In fact, the only hitter with anything close to a discipline renaissance was Richard Hidalgo, who had a 4.5% walk rate at age 19, 6% at age 20, and a solid 9.1% in the majors. No other hitter even increased his walk rate by 3% from age 20 to the big leagues. The MLB walk rates were, however, slightly higher on average than the age-19 or age-20 ones, so if Nunez makes it, it's not as if he's slated to be a Jeff Francoeur-esque hacker.

Likewise, no hitter reduced his strikeout rate by more than 6% from age 19 or 3% from age 20 to the majors. Juan Encarnacion pulled the nifty trick of going from 22.7% at 19 to 19.3% at 20 to 16.7% in the bigs, Russell Branyan took his rate down from 38.7% (!) at 19 to a slightly less ridiculous 32.9% in the majors, and Wladimir Balentien went from 29.7% at 20 to 26.7% in the bigs, but that trio are the only significant examples of strikeout-rate reduction. In fact, fifteen of the twenty-one hitters saw their strikeout rates rise from age 20 to the big leagues. That's all the more reason for Nunez to work on cutting down on the strikeouts now, because it seems he's destined for a 25%+ strikeout rate if he doesn't start making progress in the very near future.

Of course, how often these twenty-one hitters walked and struck out is not the final say on how effective they proved to be at the plate. Seven (Russell Branyan, Prince Fielder, Jay Bruce, Ryan Klesko, Richard Hidalgo, Cliff Floyd, and Matt Kemp) became .200+ ISO hitters, and Logan Morrison, Kelly Johnson, Derek Bell, and Juan Encarnacion became solid regulars. The other ten players--Butch Huskey, Alex Escobar, Wily Mo Pena, Ian Stewart, Colby Rasmus, Lastings Milledge, Travis Snider, Javier Valentin, Corey Patterson, and Wladimir Balentien--have ranged from solid to disappointing at times.

Does age-19 BB/K predict MLB wOBA for these 21 hitters? You bet it does:


Now, Matt Kemp became a hell of a hitter in spite of a .24 BB/K at 19, and Branyan was pretty good in spite of a .23 mark. Hidalgo also went from a sub-.3 mark to a very nice career. Likewise, Rasmus, Valentin, and Stewart all had K/BBs better than 2/1 at 19 and ended up struggling in the bigs (though Valentin hit well for a catcher).

Plugging in Nunez's current .22 into the formula given, we get a .321 wOBA projection for him.

How about age 20 BB/K vs. wOBA? Glad you asked!


Pretty much the same deal. We got values of .28 and .32 for Nunez's projected age-20 BB/K earlier, so if we plug those in we get .323 and .325 as his projected MLB wOBAs.

So it looks as if this extremely crude comparable-based projection system is telling us that if Nunez can navigate the minors well enough to deem himself worthy of extended MLB play, he projects as a slightly below-average hitter, with the chance for possibly being solid-average if things work out. It does seem that his chances for stardom are quite slim due to his lack of ability to control the strike zone; a further demerit is his lack of standout defense (even if he cleans up his work at third, it's not like he's playing a premium position). However, it doesn't seem that his problems are so egregious as to rule out the possibility of his becoming an effective hitter. Contrary to popular belief, though, these numbers do seem to indicate that Nunez is best served making significant statistical progress sooner rather than later in spite of his youth. He will likely always be a high-strikeout player with below-average to average plate discipline, and he'll need to show that he has the power to counteract that, as well as a glove that won't make him a defensive liability. He remains an interesting prospect who ranks just outside of Oakland's first tier of farmhands, and it's great to see him performing well in Low-A as a teenager; both extreme positivity and negativity should be tempered at this nascent stage of his development, but keep a close eye on Nunez over the next 15 months, as his career picture should become much clearer.