By Michael Bond '25
Introduction
Shohei Ohtani took the MLB by storm in 2021, winning the American League MVP in his first season free from injury and rehab limitations since his impressive rookie debut three years prior. Before he was dominating the American game, Ohtani put together a decorated career in his home country of Japan. His time in Japan’s Nippon Professional Baseball (NPB) gave him an opportunity to polish his pitching and batting skills before making the jump to harder competition.[1] His success, and that of other baseball legends such as Ichiro Suzuki, highlight the merit of the NPB within the international baseball community. This paper aims to compare the NPB with the MLB, and discuss how league structure and rules affect trends of team success.
The inspiration for this research comes from my own experiences with Japanese baseball. I spent this past fall studying in Osaka, and had the chance to attend a home game for the eventual Japan-Series champions, the Orix Buffaloes. I also attended a baseball-themed event at the US embassy in Tokyo, where I met the first Japanese player in the MLB, Masanori Murakami.
Generalizations about cultural differences between American and Japanese baseball have long surrounded discussion of the NPB, which this paper seeks to avoid. Instead, league structure and team metrics will be compared in order to discuss variations in each league’s competitive environment.
Data and Methods
This paper focuses on MLB and NPB seasons since 2010. Advanced stats are collected from fangraphs.com and npbstats.com for the MLB and NPB respectively. Baseball-reference, and the NPB’s website, are used for basic stats such as wins, losses, and playoff appearances. All data visualization is done in Python using the Seaborn and Matplotlib libraries. Regression and general data organization is through the Pandas and Scikit-Learn libraries.
For the purpose of comparison, winning percentage is used instead of wins alone.[2] This also adjusts for draws, which occur in the NPB after 12 innings. Draws exist in large part due to train schedules in Japan, which set something of a hard deadline for evening matches to finish. In 2020, extra innings were removed entirely due to coronavirus protocols.[3] For this reason, and other format changes due to the pandemic, 2020 is not included in the dataset for either the MLB or NPB. For measuring the general production of position players and pitchers, Wins Above Replacement (WAR) is used.[4] For batting, Weighted Runs Created+ (wRC+) is used, especially since it is adjusted for ballpark differences.[5]
Results and Discussion
One of the starkest differences between the two leagues comes from their overall size, and the size of their postseasons. Compared to the 30 MLB teams, there are only 12 teams in the NPB, split between the Pacific and Central Leagues. These differences are quite noticeable when looking at the distribution of Winning Percentage between the two leagues. In the regular season, NPB teams generally hover closer to the .500 mark when compared to the MLB. The format of the NPB draft, and postseason structure may also contribute to this result.
Unlike the MLB, or any major American professional sport for that matter, the first round of the NPB draft is simultaneous. If multiple teams have the same selection, a lottery system decides who gets the player.[6] The process repeats until every team has picked a player. Due to this format, no team is guaranteed the right to select the top prospect. This ultimately removes the incentive to ‘tank’ for a top pick.
In the NPB, the top 3 teams in each league make the playoffs, or half of all teams. In comparison, the MLB playoffs welcomed only 12 of 30 teams in 2022, and even fewer in previous years. The simplified playoff structure in the NPB makes it less common for a team to miss the playoffs with a winning record. Within the included seasons, it has only occurred 5 times in the NPB, but 55 times in the MLB. This may keep organizations in the NPB invested in the season, as they are likely not too far out of playoff contention. Ultimately, reaching the playoffs is far more difficult in the MLB, as seen in the extremely high winning percentages of MLB teams.
Another topic worth discussing is the balance of power between pitchers, batters, and positional players generally. For position players, we see a very similar distribution of WAR for both leagues. Both also share a positive correlation between WAR and winning percentage, but the correlation is slightly stronger in the NPB. Furthermore, similar relationships occur with wRC+. It is also interesting that there are multiple outlier MLB teams with high positional WAR that did not win over half of their games.
The more noticeable difference comes from looking at these same relationships but with pitching WAR. In that case, median NPB teams have similar but slightly higher WAR. However, pitching WAR has little correlation to winning games in the NPB. In contrast, MLB pitching WAR has a near identical correlation to winning percentage as positional WAR. Among teams with a winning record, NPB teams drop to slightly below their MLB counterparts, but have a higher floor.
Conclusion
It comes as no surprise that two professional leagues playing the same sport follow similar, and often expected trends. However, differences in league structure and game rules provide an avenue for altering the competitive environment. For example, playoff and draft structure can help explain the tighter distribution of winning percentages in the NPB. With fewer teams overall, reduced competition for playoff spots, and a draft that does not significantly reward tanking, the NPB pushes teams closer towards the .500 mark instead of the extremes. In contrast, getting stuck in the middle of the MLB can be a purgatory. Teams are encouraged to make moves for the future, often improving already winning teams at the sake of their own record.
The distribution of positional and pitching WAR was originally very surprising to me. Many traditional commentaries on the difference between Japanese and American baseball posit the Japanese game as more defensive.[7] As such, I was expecting pitching to be the best predictor of success. However, this study has shown that positional WAR and wRC+ are better at predicting wins. This is even though median NPB teams have slightly better pitching than their MLB counterparts. It is possible that when most teams have relatively competent pitching cores, batting and fielding may be more useful for differentiation. This is supported by the fact that the NPB uses a smaller baseball, allowing pitchers to generate spin more easily.[8]
A comparative study such as this is ultimately a starting point for a better understanding of each league, and a discussion of potential changes. Looking towards an established and popular league such as the NPB could help the MLB implement new policies to improve the game and the fan experience. In fact, the NPB hosted more fans per game than the MLB on average in 2019.[9][10] Finally, as more notable players make the jump to the MLB, analytics surrounding the NPB will also be valuable for player evaluation. More data and research on the subject of that transition to the MLB would be interesting in the future.
[1] Thompson, “A Japanese Propaganda Film Helped Shohei Ohtani Follow a Path to Making Baseball History.”
[2] Winning percentage is calculated as (2*wins+ties)/2*games.
[3] Coskrey, “NPB Strikes out with Move to Eliminate Extra Innings.”
[4] “Wins Above Replacement (WAR) | Glossary.”
[5] “Weighted Runs Created Plus (WRC+) | Glossary.”
[6]For a summary of the NPB draft format, see 一般社団法人日本野球機構, “選択手順 | 2022年 プロ野球ドラフト会議 supported by リポビタンＤ.”
[7] For one example commentary, see Ikei, “Baseball, ‘Besuboru, Yakyu.’”
[8] “The Scientific Differences Between Masahiro Tanaka Pitching in Japan and Major League Baseball.”
[9] 一般社団法人日本野球機構, “2019年 セ・パ公式戦 入場者数.”
[10] Brown, “MLB Attendance For 2022 Down Nearly 6% From 2019, Last Year Before The Pandemic.” NPB attendance in 2022 was no longer above that of the MLB, but Japanese policies surrounding the pandemic remain far stricter than in the US. It will be interesting to see how the metrics play out in the future.
Works Cited
Brown, Maury. “MLB Attendance For 2022 Down Nearly 6% From 2019, Last Year Before The Pandemic.” Forbes. Accessed December 24, 2022. https://www.forbes.com/sites/maurybrown/2022/10/06/mlb-attendance-for-2022-down-nearly-5-from-2019-last-year-before-the-pandemic/.
Coskrey, Jason. “NPB Strikes out with Move to Eliminate Extra Innings.” The Japan Times, April 10, 2021. https://www.japantimes.co.jp/sports/2021/04/10/baseball/japanese-baseball/npb-extra-innings/.
Ikei, Masaru. “Baseball, ‘Besuboru, Yakyu’: Comparing the American and Japanese Games.” Indiana Journal of Global Legal Studies 8, no. 1 (2000): 73–79.
“The Scientific Differences Between Masahiro Tanaka Pitching in Japan and Major League Baseball.” Accessed December 24, 2022. https://www.sporttechie.com/the-scientific-differences-between-masahiro-tanak-pitching-in-japan-and-the-mlb/.
Thompson, Jackson. “A Japanese Propaganda Film Helped Shohei Ohtani Follow a Path to Making Baseball History.” Insider. Accessed December 22, 2022. https://www.insider.com/japanese-propaganda-helped-shohei-ohtani-make-baseball-history-2021-4.
MLB.com. “Weighted Runs Created Plus (WRC+) | Glossary.” Accessed December 24, 2022. https://www.mlb.com/glossary/advanced-stats/weighted-runs-created-plus.
MLB.com. “Wins Above Replacement (WAR) | Glossary.” Accessed December 24, 2022. https://www.mlb.com/glossary/advanced-stats/wins-above-replacement.
一般社団法人日本野球機構. “2019年 セ・パ公式戦 入場者数.” NPB.jp 日本野球機構. Accessed December 24, 2022. http://npb.jp/statistics/2019/attendance.html.
———. “選択手順 | 2022年 プロ野球ドラフト会議 supported by リポビタンＤ.” NPB.jp 日本野球機構. Accessed December 23, 2022. https://npb.jp/draft/2022/schedule.html.