Revisited: how much does Reno inflate hitters’ numbers?

Reno has long had a reputation as one of the most hitter-friendly parks, not just in the Pacific Coast League, but all minor-league baseball. At an altitude of 4,500 feet, the city is close to Denver in terms of altitude, and the slightly lower humidity also works in hitters’ favor. The results means that hitters playing there tend to enjoy an inflation of their statistics, while pitchers’ numbers go the other way, seeing their ERAs bloated by a high run environment. Last year, for example the Reno park factor for runs was 35% above average, second in AAA to only Colorado Springs [Also worth noting, five parks in the PCL had higher park factors for runs than any International League team]

This means we have to be cautious when looking at the stats produced by Aces’ hitters, because history shows us they typically take a significant hit when those players move to the major-leagues. It has been a known issue almost since the D-backs moved their Triple-A affiliate from Tucson in 2009. Five years ago this month, we took a look at the numbers, comparing how the same hitters produced at AAA and in the majors. The conclusion: “Moving from Reno to the major-leagues will knock about 80 points off your batting average, 100 from your OBP and deduct 140 points off your SLG, for a total loss of 240 points from the expected OPS.”

That was in June 2012. Acknowledging the issue, before the 2014 season, the Aces became the fourth professional team to install a humidor at their ballpark, following the Colorado Rockies and the PCL teams in Colorado Springs and Albuquerque. [El Paso and Salt Lake have also done so now] Has it had an impact? As a quick and dirty check, let’s look at the total number of runs scored and home-runs allowed (home and away), by the Reno hitters and pitchers respectively, over the four seasons from 2013-2016. Remember, the first year below was before the humidor was introduced, and the other three came after.

• 2013: 757 runs scored, 129 home-runs allowed
• 2014: 790 runs scored, 121 home-runs allowed
• 2015: 758 runs scored, 117 home-runs allowed
• 2016: 726 runs scored, 120 home-runs allowed

I’m hard-pushed to spot much of an immediate change. Yes, home-runs seem to have declined slightly, but it hardly seems a dramatic decrease. Still, if we’re going to look at evaluating numbers put up by Diamondbacks prospects in Reno, we should see if the difference has changed since our original study, and confine ourselves to the numbers since the beginning of the 2014 season. Of course, we’re rapidly heading towards another change in environment, with a humidor now under construction at Chase Field. So we’ll likely need to revisit these numbers once again, down the road, and compare humidor against humidor!

The methodology is pretty much as it was five years ago. We look for players who have had at least 50 at-bats in the same season, both with Reno and the big-league club. This is to minimize the impact of player development and aging. We include both prospects who were called up to the big-league club, and major-leaguers who spent significant time in Reno, on rehab or other assignment. The chart below shows a summary of their triple-slash numbers and PAs in each environment. [For anyone interested, or who wants to do further work, here is the full sheet] On the left are the Reno numbers, on the right the ones in MLB.

In summary this is what we find, based off a total of about 3,200 plate appearances for Reno, and roughly half as many in the majors.

• 2012: .307/.392/.517 = .909 OPS vs. .226/.296/.374 = .670 OPS
• 2017: .304/.365/.476 = .841 OPS vs. .222/.272/.344 = .616 OPS

The variation in raw numbers can be attributed to the studies involving significantly different groups of players, obviously. But I’m amazed, given that, at how little difference there is between the two samples. The downgrade across the triple-slash between AAA and Reno five years ago was .081/.096/.143, for a .239 drop in OPS. Now, the same differences come out to .082/.093/.132, for a .225 drop in OPS. And the gap would have been even closer to that of 2012 - at .228 OPS, to be exact - before Rey Fuentes’s extra-inning home-run on Sunday. :)

There is an interesting trend here, however. While across the 2014-17 period, the difference didn’t change much, in the first two seasons after the humidor was introduced, the gap between AAA and MLB performance did narrow significantly. We should be cautious, because we’re basically slicing the sample size in half. With that said:

• 2014-15: .302/.372/.434 = .806 OPS vs. .235/.285/.337 = .622 OPS
• 2016-17: .306/.357/.528 = .884 OPS vs. .191/.240/.360 = .600 OPS

Over the initial two years, the gap between Reno and Phoenix dropped to 184 points of OPS. But over the last two years, it has rebounded a full hundred points, back even beyond the figure in 2012, and has been a whopping 284 OPS points. I’m curious if there has been any change in environment, between the 2015 and 2016 seasons, which might have led to the sharp uptick.

This does mean we should perhaps be even more cautious about evaluating results by prospects in Reno. We’ve seen this with Rey Fuentes, and let’s also look at Ketel Marte. He has been raking in Reno, with a line of .358/.407/.541 which has prompted calls for him to be promoted. But, hold on... If we apply the 2014-17 correction to those numbers, it projects to an MLB equivalent of .276/.314/.409, for a .723 OPS - basically identical to that of Nick Ahmed this season (.721). And if we apply the larger 2016-17 adjustment, Marte’s projected triple-slash plummets to .243/.290/.373, a .663 OPS which is closest to Chris Herrmann territory (.639) on the D-backs this year.

It’s certainly something to be taken into account. I know that, personally, I’ve been burned by shiny AAA numbers enough, it now takes something really gaudy for my skepticism to be overcome by enthusiasm!