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De-Humidor, Deflategate and An Unexplored Advantage

Red Sox hitters currently rank 30th in baseball in BABIP, and it’s really not that close. Their .257 mark through Saturday is partly a function of bad luck, almost certainly, but it’s also partly a function of a poor line drive rate (24.25%, 25th) and an obnoxiously high rate of popups (8.66%, 3rd). Despite the crazy gap in BABIP — Seattle is next worst at .269 — Boston’s offense hasn’t been completely atrocious. Add in the majors’ second-best walk rate and you get part way toward explaining why that BABIP albatross hasn’t prevented the team from scoring 4.08 runs per game, just under league average.

But to some extent, the Red Sox’s BABIP may always be a bit lower than their batting average would lead us to expect. After all, they play half their games in a park where this can happen:

That bit of thunder from Allen Craig’s boomstick had an estimated “true distance” of 326 feet. In only six parks would that have even hit the wall, and I’m going to go ahead and guess that at PNC Park and Progressive Field (both 325 feet), 326 feet still means “in play.” I know what you’re thinking, so I’m going to save you the time: 325 feet at McCoy Stadium.

The point is that ballparks provide some inconsistencies that you don’t have in other sports, including, say, football. Game conditions can change in football, just as in baseball, but I wonder if even that doesn’t make as much of a difference; hitters don’t have quite as much control over a ball’s trajectory in the first place as a quarterback would have. Especially if footballs were especially easy to throw for some reason.

In last week’s edition of Read Sox, Nick Canelas addressed the close connection between Deflategate and MLB’s new ball “security and storage” policy. Apparently, MLB sent a memo to teams before the season with a “nine-step procedure on ball handling” according to this AP report. From the AP report:

“Obviously, there’s not as much that you can do to baseballs,” Los Angeles Angels pitcher C.J. Wilson said. “I mean, you can’t change the density of the baseball at any point — unless you dunk them in water. Then they’re going to be 9 ounces, and everyone’s going to blow their arms out.”

As right as he’s been on hair products, I have to disagree with Wilson here. Water isn’t always a liquid, and although water vapor can’t get shampoo out of your hair, it can affect the baseball. The results are not trivial.

And weight is only part of it. In a guest piece about humidors at Baseball Prospectus four years ago, Dr. Alan Nathan explained how absorption of water can affect batted ball velocity. Published lab experiments tell us that in terms of balls hit hard enough to become home runs, baseballs stored at 50% humidity lose about 0.6 mph in batted ball velocity as opposed to balls stored at 30% humidity (used as an approximation for Denver). But humidity also affects baseballs in another, more meaningful way: it’s also about how a “mushier” ball has a lower coefficient of restitution (like a Chicago-style softball). The decrease in bounciness for the same ball would mean about a 2.2 mph difference in batted ball velocity.

From what we’re starting to see from newly-available batted ball data this year, this is probably not just about home runs — many of the grounders we see are hit just as hard as home runs (definitely a lot more than I had thought), and overall velocity seems to have a huge effect on how frequently a ball falls in for hit. It seems to really matter, although with fielding in the mix (unlike with home runs), it may be a while before we can confidently start to draw conclusions about the extent.

In the BP piece, Dr. Nathan suggested that the Coors Field humidor has likely reduced home runs there by 30±6 percent. The potential effect of a humidor at Chase Field could be even more significant; Phoenix is twice as dry as Denver. Boston, on the other hand, is in some months as different from a humidor as Denver is — just in the other direction. Although the Denver humidor suppresses offense by increasing the humidity of baseballs, 50% humidity storage in Boston would mean a decrease — and the ball would travel farther.

One good thing about calculating reductions in home run distance is that you already know which batted balls to use. The flip side isn’t exactly true; the point would be that some of the fly balls that died on the track might end up over the fence. But looking specifically at balls that were already home runs and assuming that Dr. Nathan’s distance calculations would be linear even if in the other direction, I took a look at the possible effect of humidors at all MLB parks in a piece at Beyond the Box Score last November.

Some of the results: -13.1 feet on home runs balls in Denver becomes +7.9 feet in Boston, as a humidor might reduce the humidity of baseballs from 59% (average in Boston from April to September) to 50%. I’m not sure exactly how fence height plays into this for fly balls that have almost come back to earth (I’m estimating with a 30 degree angle), but while that Allen Craig home run might only have been over the fence in two or three parks, it looks to me like another eight feet might have put it over in 15 of 30 parks. Like I said: not trivial.

Although the Denver humidor suppresses offense by increasing the humidity of baseballs, 50% humidity storage in Boston would mean a decrease — and the ball would travel farther.

According to the AP report, the MLB memo from before Opening Day specified 50 percent humidity for baseball storage. That makes complete sense: it’s the exact level that Rawlings itself uses for its baseball storage, and for that reason, it’s what the Coors humidor is set at. It’s also what I assumed in that Beyond the Box Score exercise. But if the Red Sox wanted baseball storage at that level, it wouldn’t require adding moisture as in Denver, but taking moisture out of the air.

I have no idea how the Red Sox store their baseballs right now, so take all this with that caveat. But even if the team does have a “de-humidor” that is inspected and used just before games, that doesn’t end the inquiry.

Last year, Dr. Nathan kindly confirmed that it is almost certainly more appropriate to use an average of average daily humidity levels, rather than an average afternoon humidity level — the humidity of the air can fluctuate enormously, and it gets lowest when things get hottest, making early afternoon generally the driest part of the day. Dr. Nathan noted that it took about three days for a ball to acclimate to the air in laboratory settings.

From the AP report, it seems like the balls are closely supervised — but only on the day of the game. Balls ticketed for the umpires’ room are in storage prior to that. So what happens then? And for that rate, what about the air going into the umpires’ room? Maybe there was a memo requiring them to be hermetically sealed after Jason Grimsley’s adventure in 1994, but I’m guessing there’s an air vent that, you know, air could get through.

Baseball’s version of Deflategate didn’t come in the playoffs, but in September 2010 when Tim Lincecum had some colorful things to say about the Rockies supposedly switching balls mid-game. MLB took the ball-fetching part of the procedure out of the Rockies’ hands, and with the memo this year did the same for everyone. Now, it’d be like letting the grass get long if you think you’re relying on ground ball pitchers, or watering the infield if you’re slower than the other team: if it might affect one team more than the other (fly ball pitcher coming to town?), it can still be an advantage.

Which is all to say: there’s still the potential for shenanigans here. Kudos to MLB for making a change in recognition that the Rockies aren’t the only team that could manipulate the humidity of baseballs to gain an advantage, but the Red Sox can still act the fox. Regardless of how the balls are stored, the balls turned over to the umpires’ room on Friday are stored in the henhouse for meaningful days beforehand.

Photo by Tommy Gilligan/USA Today Sports Images

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