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Projecting the NPB to MLB Transition for Batters

How might a position player from the Nippon Professional Baseball League fare if they were to venture to the MLB?

Yoshio Itoi
Yoshio Itoi
Atsushi Tomura/Getty Images

Ever since Alex Chamberlain posted this great article at Fangraphs looking at how Cuban players have performed in the MLB, I was interested to see how the same process might apply for Japanese players. Examining transitions from Cuba to the USA by comparing a batter's last season in Cuba to their first season in the USA makes it easy to see how a player like Yasmany Tomas might struggle at first. His strikeout rate (K%) in Cuba was way above average and his walk rate (BB%) was well below average. Both statistics are likely to be exaggerated further in the MLB. In his article, Chamberlain contemplates the risk associated with the Cuban market and how the sudden boom in productivity will lead teams to overspend to acquire talent from the island. Japan may represent a similar profile.

Unfortunately, rumors of more Japanese players making the journey to play in the MLB this year fizzled out after some speculation. In 2014, we saw pitching ace Masahiro Tanaka sign with the Yankees, but position players making the move have been more scarce. Norichika Aoki and Munenori Kawasaki were the last batters from the NPB to come over to the United States. They came over in 2012.

There are obvious reasons for the lack of player transition. The Nippon Professional Baseball posting system is an arduous process for teams to go through, and understandably so. The NPB does not want to lose their baseball talent to the MLB before their own teams can have a run at a championship with their star players. So international dealing is very restricted. The restrictions work the other way as well. NPB teams cannot have more than four foreign-born players on their 25-man rosters. In addition to all of this, eligibility for international free agency requires nine seasons of service time in the NPB. This means that players cannot openly sign with an MLB team without undergoing the posting system unless they have met the required service time. After nine seasons, much of the talent has degraded.

Despite all of the obstacles, twelve batters have bridged the leagues and been given at least 100 plate appearances in the MLB. Using those twelve players, I attempted to form a conclusion on the NPB to MLB transition. This chart, ordered by the change in K-BB% across leagues, contains the plate discipline data for the players in their last season in the NPB, first season in the MLB, and the change (MLB K-BB% - NPB K-BB%).

NPB to MLB Stats

Interestingly, the average strikeout rate doesn't change much at all. The change data vary widely, with a range of -5.63% to 4.04%, but it is not clear that there is a change in one specific direction. Different batters take to the MLB differently and the data have yet to (and perhaps never will) point to a drastic uptick like one might expect. Walks are a different story. On average, Japanese batters walked 2.9% less in their first season in the MLB, which is significant enough to have a profound impact on a batter's performance. Backing these data up is the fact that NPB batters walk more often than do batters in the MLB. In the US, pitchers had a 2.9 BB/9, but in Japan, pitchers had a 3.2 BB/9 in 2014. When these players were exposed to MLB pitchers their walk rates decreased accordingly. Nippon Professional Baseball is slightly more offensively skewed than the MLB, and so batting statistics have to be slightly downgraded when comparing the two leagues.

On that note, many of Japan's teams are trying to boost their offensive performance. Home runs fill stadium seats and baseball plays a large role in the Japanese economy. For example, Jim Allen explains that the Fukuoka SoftBank Hawks are moving in their fences for the 2015 season in order to have more home runs during their home games. The chart below (sorted by change in isolated power [ISO]) compares the same sample of batters on measures of BABIP, HR%, and ISO for the seasons on either side of the transition. HR% is a measure of how many batted balls became home runs, excluding all forms of sacrifice hits.

NPB to MLB Stats2 Fixed

More trends become clear from this chart. On average, BABIP drops, HR rate drops, and ISO drops. It's hard to estimate why BABIP might drop from one league to another but I would guess that it is a result of the quality of defense. If you were to judge the two leagues by fielding%, you would come to the conclusion that they are about equal but fielding is so much more than simply errors and putouts. Range, arm strength, ball transfer, and ball tracking all play into defensive value. Deeper analysis of MLB-level defense awaits higher quality tracking software, but for now, I'd mark the drop in all three categories down to better fielding and perhaps weaker contact.

All this being said, the observed drop in performance makes sense given that the NPB is referred to as a AAA-level league in comparison to the MLB. In the next part of the two part series, I'm going to use these findings to project what a couple of NPB players might produce in the MLB. I will be using Kazuto Yamazaki's NPB Prospect Rankings to determine which five batters will get tested. Stay tuned.

(This is part one of a two part series. Check out part two here.)

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All statistics courtesy of FanGraphs and Baseball-Reference.

Justin Perline is a writer for Beyond the Box Score and The Wild Pitch. You can follow him on Twitter at @jperline.