Is Japan's Professional Baseball League Unfair?

"I was always pitching to a smaller strike zone," Ryan Vogelsong said of his time in Nippon Professional Baseball. "That's just the way it is, it's the unwritten rule of baseball there, the foreigner's strike zone is going to be smaller."

Vogelsong is not alone -- other returnees from Japan report unfair treatment from umpires there. A first look at the numbers seems to hint at the possibility that the strike zone is called differently for Japanese and foreign players. But closer inspection reveals that this could also come from a clash of cultures -- baseball cultures.

Last Friday, Giants Ryan Vogelsong and Casey McGehee -- while highly appreciative of their time in Japan and the things they learned while playing there -- both independently referenced preferential treatment for homegrown stars in Nippon Professional Baseball.

From the other side of the plate, McGehee said that "you end up striking out looking a lot because there were a lot of times that if the catcher caught it, you were sitting down." Using the Japanese word for foreigner, McGehee said the matchup was important: "Your best case scenario was when you had a gaijin pitching and a gaijin hitting."

Jason Coskrey covers baseball for the Japan Times and has heard foreign players say this sort of thing before. He reached out to Jeremy Powell, who was with the Expos for two years and pitched in both NPB's Central and Pacific Leagues from 2001-2008. While Powell felt that umpires were "focused on simply doing their best to do a good job," it was a bit different when it came to big calls -- "in crucial counts that really had an impact on how the inning may end up there were times that the call would favor the native player -- it came with the territory (literally), it's part of the game and I had to move on, albeit it was never easy."

The anecdotal evidence lines up, but this is a tough one to study through the numbers. Without the strike zone plots PITCHf/x affords us here in America, we're left looking at results. We can say that, in NPB, foreigners strike out 18.7 percent of the time compared to the 18.4 percent of the time that native Japanese batters strike out, but those numbers are full of bias. Selection bias at the very least -- there are a lot of fading sluggers that leave Major League Baseball go to Japan, and it's certainly possible that the sample isn't full of kings of contact.

But we can match players that played both in Japan and in America and separate them into two buckets based on their nationalities. Brian Cartwright makes Major League Equivalency lines for his OLIVER projection system all the time, and so he ran the numbers to see if the multiplicative factors were different in the different sets of position players. They were, especially so in two important cases.

Using multiplicative factors, you need to divide a foreign batter'€™s NPB strikeout rate by 1.083 to get his MLE. A Japanese batter's factor is 0.954. This is caused by foreign batters striking out at a disproportionate rate in NPB. In fact, these 167 foreign batters struck out more often in Japan than elsewhere, while the 50 Japanese batters struck out less. The walk rates reinforce what was found looking at the strikeouts. The two stats, taken together in a regression analysis, suggest that foreign batters are in fact seeing more strikes (64.3 percent to 63.3 percent).

As tempting as it might be to hold on to these small differences and call them definitive, we still aren't sure there's bias based on nationality in NPB. The game is taught slightly differently in different countries, or different things are valued slightly differently at least, and there's still a possibility that there's just a disconnect between the American style of play and the Japanese style of play that's mucking these numbers up.

For instance, let's look at swing rates. Players in MLB last year swung at 47 percent of the pitches they saw. Patrick Newman of NPBTracker found that batters swung at 63 percent of the pitches they saw in NPB in 2012. A group of players bred to play a certain way may have different results in a new league that plays differently. That's how your strikeout rate might go up more than you would expect.

Or: if you put a newcomer bred to be patient with pitches around the edges with no track record and no acquired knowledge of the way the strike zone is called into an established league built on playing to contact, it shouldn't be surprising if there are some differences of opinion when it comes to how the strike zone is called.

As Powell himself admitted above, much of his opinion is also built on high-leverage moments where the call went the wrong way. Those are emotional moments. As psychologists Sven-Ã…ke Christianson and Elizabeth F. Loftus found in a seminal 1990 study, we remember emotional moments better.

There's some evidence of systematic differences in the Japanese strike zone, but we're guessing at the root causes. Contributing to the feeling of unfairness is a combination of a few high-profile moments with lasting influence and a possible difference in baseball cultures. We still can't be sure, especially in a league that is only now beginning to enter the PITCHf/x era themselves. As the strike zone is more clearly tracked, we should be able to both understand this phenomenon better and possibly correct it, should it be shown to truly exist.