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  • Writer's pictureBruin Sports Analytics

Shohei Ohtani and the Emergence of Japanese Talent in the MLB

By: Jason Vo

Source: AP Photos

On March 21, 2023, in the 9th inning of the World Baseball Classic Championship with 2 outs and no runners on base, Team USA’s Mike Trout came up to bat against Team Japan’s Shohei Ohtani representing the tying run. Both were teammates on the Los Angeles Angels, and the likelihood of this situation being so perfect was one in a million. This was the moment all baseball fans had dreamed of; arguably the best American player in the modern era MLB against, undoubtedly, the greatest Japanese player to ever play in the MLB. This was baseball’s version of LeBron James and Michael Jordan playing each other.

While Ohtani eventually struck out Trout on three swing-and-miss strikes, this game watched by 4.5 million worldwide failed to answer a question asked by many leading up to the game: Was Japan and its Nippon Professional Baseball (NPB) slowly overtaking the MLB for the best players and more specifically, pitchers? While history has shown dominance of MLB pitchers compared to NPB over many years, we took a deep dive into how the gap has widened between NPB/Japanese pitchers migrating to the MLB compared to traditional MLB pitchers over the past 25 years.

The criteria for selecting NPB-turned-MLB pitchers was that an eligible Japanese pitcher had to have pitched at least 1000 innings, despite years played in the MLB. This decision was made to support the fact that innings pitched are considered more appropriate for including potential irregularities, such as one-season wonders, which is still considered “good” data for the question we are answering. For pitchers who began their career in the MLB, the decision was made to choose the best pitchers over the past 25 years. Thus, Cy Young winners, the award given to the best pitchers in each league, were chosen. There are notable names omitted from selection that have never won the Cy Young award, such as Gerrit Cole. However, non-award winners were kept in order to maintain consistency among data and prevent personal bias. For the sake of convenience, Japanese pitchers will be referred to as NPB pitchers and non-Japanese pitchers will be referred to as MLB pitchers. Since there are pitchers used in this data that are still active players, this data is accurate as of May 5, 2023.

This article will take a deeper dive into the following advanced baseball statistics to determine the influence of NPB and MLB pitchers.

WAR (Wins Above Replacement) - How many more wins a player is worth to the team compared to a replacement-level player; AKA player’s contributions to the team

WPA (Win Probability Added) - Pitcher’s performance on the outcome of a game, 1 WPA means 1 win added

K/BB (Strikeouts/Base On Balls) - Strikeout to base on balls ratio; 9 K/BB means 9 strikeouts for every 1 base on ball


The simplified dataset includes notable Hall-of-Fame pitchers such as Roger Clemens, Pedro Martinez, and Randy Johnson, who delivered career outings during their prime seasons.

Clemens' 271 strikeout 1997 season resulted in an incredible WAR of 11.9, highlighting his immense impact on the field, despite the team not seriously competing for the title. Similarly, Martinez's dominant 1999 season generated a WAR of 9.8, as he finished second in MVP voting and led the MLB in K/BB that season with 8.46. Randy Johnson's 2002 season yielded a formidable WAR of 10.7, with 300 plus strikeouts and 24 wins. These elite MLB pitchers consistently delivered quality starts and significantly contributed to their teams' success, regardless of how much offense their own team provided.

On the other hand, regarding Japanese-born pitchers in MLB, the analysis focuses on the best seasons of players like Yu Darvish. His sophomore 2013 season produced a respectable WAR of 5.6, demonstrating his ability to make valuable contributions to his team, despite only having a 13-9 win-loss record. Shohei Ohtani, the two-way phenom that broke out in 2021 with an MVP caliber season, fielded a 6.2 pitching WAR in the following 2022 season breaking several club records and pitching an impressive 2.33 earned run average.

Comparing the two groups, MLB pitchers tend to exhibit higher average WAR values in their best seasons compared to Japanese-born pitchers. This discrepancy may be due to several factors, including differences in the level of competition between MLB and the NPB, variations in playing styles, and the adjustment period required for Japanese pitchers to adapt to the MLB's distinct environment. The MLB is known to be the best baseball league in the world, and, thus, the best players from Japan may not always turn out to be like Shohei Ohtani and dominate the game right away or even at all. There are significant differences between the playing styles of both leagues, as the NPB values contact and more of an emphasis on strategy with bunts and such, compared to the MLB and its trend of homeruns or strikeouts every at-bat. In a 2017 study comparing contact rate in the NPB and MLB, the NPB contact rate at 78.9% was higher than the MLB rate at 77.5% while the NPB also had a swinging percentage of 45.8% compared to the latter 46.5% (Sarris 2017). This exemplifies the fact that NPB players tend to be more selective in swinging and making contact, while the MLB displays less taking of pitches and more swinging. It’s important to note that there also is an “acclimation” period for Japanese pitchers and it's common for overseas players to struggle in their first few seasons before breaking out like Darvish or Ohtani in the subsequent years.

Despite this comparison, it is important to consider the limitations of the dataset and the context surrounding the WAR metric. While WAR provides a valuable measure of overall player contribution, it may not capture all aspects of a pitcher's performance or their specific impact on team success. Other factors, such as team support, defensive capabilities, and run support, can also significantly influence a pitcher's performance and should be considered when evaluating their overall success. For instance, a pitcher could potentially throw seven innings, while giving up a single run, but if the team does not support him with runs, then the pitcher still can be credited with a loss. Also, the MLB has very much changed from when Randy Johnson used to pitch until now. As a result, it’s only appropriate to compare each player with one another to an extent, and to keep in mind the competition that each player played against.

The analysis of the provided data suggests that, on average, MLB pitchers' best seasons tend to yield higher WAR values compared to Japanese-born pitchers who transitioned to MLB. This doesn’t undermine the longevity of Japanese-born pitchers' careers, who have successfully competed at the highest level of professional baseball for years. Further comprehensive analysis, considering a broader range of data and incorporating factors, like team support, would provide a more thorough understanding of the success and impact of Japanese-born pitchers in MLB.

WPA and K/BB

The scatterplot visually compares the performance of MLB and Japanese-born pitchers in Major League Baseball (MLB) based on their Win Probability Added (WPA) and Strikeouts/Base On Balls (K/BB) ratio. The plot showcases the relationship between these two metrics and highlights potential differences between the two groups. These variables are appropriate to compare since the main goal of a pitcher is to strikeout as many batters as possible while limiting the number of walks. One would assume that the more strikeouts and less walks that a pitcher issues, the more WPA a pitcher has. Looking at the plot shows that this is not always the case.

Observing the scatterplot, it becomes apparent that MLB pitchers are more widely distributed across the graph, occupying a larger range of WPA and K/BB values. This suggests a greater variability in their performance compared to Japanese pitchers. This makes sense in the context of this data. To win the Cy Young award, a pitcher doesn’t need to have the most strikeouts. The pitcher simply has to be the best and most dominant. Thus, there are pitchers who are contact pitchers, or pitchers who make their living on groundouts and flyouts.

Also, unlike WPA where the stat is a cumulative number of win probability added during the entire career of a pitcher, K/BB is a stat that may be influenced by the non-prime years of a pitcher. More specifically, the youth and “washed” seasons may significantly lower the K/BB of a pitcher who was dominant in their prime years. On the other hand, the Japanese pitchers exhibit a more concentrated grouping, particularly in terms of K/BB ratio, with most falling within the lower to mid-range values. This makes sense since Japanese pitchers are mostly consistent year-to-year and are taught to simply get outs rather and be more conservative rather than throwing over 100 MPH and gathering high strikeout rates.

For WPA, both MLB and Japanese pitchers have varying degrees of success, as indicated by the distribution of data points across the x-axis or the WPA line. However, it is worth noting that a few American pitchers exhibit notably higher WPA values, suggesting that MLB players are more dominant and are more impactful to the game, whether the pitcher is a high strikeout rate flamethrower or a pitcher that can give you six innings with no runs. Meanwhile, Japanese pitchers tend to exhibit a more consistent level of performance, with a narrower range of WPA values. Once again, this follows the Japanese trend, as players are taught to simply do their job, with the exception of game changing pitchers that have come through Japan, such as high-quality starters Ohtani, Darvish, and Tanaka, as well as once a shutdown closer for the Red Sox, Koji Uehara.

Regarding the K/BB ratio, the scatter plot reveals an interesting contrast. American pitchers exhibit a broader range of ratios, with some achieving relatively high values, indicating a strong ability to strike out batters while minimizing walks, while others achieve very below-average K/BB ratios. On the other hand, Japanese pitchers tend to cluster around a more moderate range of K/BB ratios, indicating a balanced approach with fewer extremes. MLB pitchers tend to have higher velocity on their pitches and, most of the time, less control, leading to very low K/BB numbers because of the lack of consistency among each batter faced. NPB pitchers, on the other hand, utilize control more effectively and instead of overwhelming the batter with velocity, Japanese pitchers use breaking balls to retire the batter.

Overall, the scatterplot allows us to visually compare the performance of American-born and Japanese-born pitchers in terms of WPA and K/BB ratio. While American pitchers exhibit greater variability and potential for exceptional performance, Japanese pitchers showcase a more consistent and balanced approach. This analysis provides valuable insights into the differing pitching styles and performance characteristics between these two groups in the context of MLB.


In summary, the scatterplot comparing American-born and Japanese-born pitchers in MLB provides valuable insights into their distinct characteristics and performance patterns. The plot reveals that American pitchers exhibit a wider variety of pitching outcomes in terms of Win Probability Added (WPA) and Strikeouts/Base On Balls (K/BB) ratio, indicating both exceptional pitching outings and a lack of consistency among keeping walks at a minimum. Conversely, Japanese pitchers demonstrate a more consistent and balanced approach, with narrower ranges observed in these metrics.

For up-and-coming pitchers, such as Roki Sasaki of the NPB, the trend of MLB pitchers being outright better than Japanese pitchers may not hold true for much longer. Much like Shohei Ohtani, Roki Sasaki is projected to be the next Japanese star to leave to the MLB once his NPB contract is up. The 21 year old phenom, who pitched a 19 strikeout perfect game at the age of 20, possesses a 100 MPH fastball. He became a household name during Japan’s WBC title run, and some predict that, while he may never be as dominant or as impactful or a player as Shohei Ohtani, Sasaki may have a better pitching career than his Japanese counterpart. While we may see his debut in a couple more years, as of right now, one thing is for certain. While Shohei Ohtani and the rest of the current Japanese players are not quite on the same level as MLB pitchers, the country of Japan is making a name for itself in the pitching world, and pretty soon, Japan may be an outlet for producing hall of fame careers for pitchers.


“Advanced Stats: Glossary.” MLB.Com, Accessed 16 June 2023.

Baseball Almanac, Inc. “Major League Baseball Players Born in Japan.” Baseball Almanac, Accessed 16 June 2023.

“MLB Stats, Scores, History, & Records.” Baseball, Accessed 16 June 2023.

Sarris, Eno. “Baseball in Japan Is Surprisingly Similar.” FanGraphs Baseball, 11 Dec. 2017,



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