Interpreting Foreign League Statistics: Sabermetrics Glossary for Fantasy Baseball (2025)

March 27, 2025

What tools are available for foreign leagues and how to use sabermetrics for fantasy baseball? An in-depth overview of the Korean Baseball Organization (KBO) and Nippon Professional Baseball (NPB).

Welcome, RotoBallers, to our primer on interpreting foreign league statistics. This article is a deeper dive into how to interpret foreign statistics and is part of our ongoing series "Using Sabermetrics for Fantasy Baseball."

In this article, we'll focus on statistics from the Korean Baseball Organization (KBO) and Japan's Nippon Professional Baseball (NPB). Imports from both leagues generate a lot of hype and fantasy interest, and this article will help you establish reasonable expectations for them.

You can find our entire sabermetrics glossary, which includes links to many other sabermetric stats, as part of this series. Good luck in 2025!

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Interpreting Foreign Statistics: Sabermetrics Glossary

Major leaguers are on every fantasy manager's radar, and minor leaguers are as well. However, there's still one player pool that you might not be familiar with.

There are international leagues outside of MLB, with imports making a huge impact for real-life MLB clubs and fantasy gamers. Kodai Senga finished second in Cy Young voting in 2023. Shota Imanaga won fantasy leagues last year. Yoshinobu Yamamoto was elite on a per-inning basis in 2024.

Of course, not every import is a home run. The Red Sox tried to trade Masataka Yoshida with no takers. Jung Hoo Lee wasn't lighting the baseball world on fire before an injury prematurely ended his debut season.

Fortunately, fantasy managers have the tools to determine what to expect from these imports. Let's learn how to use them!

A Primer on the Korean Baseball Organization (KBO)

The KBO is famous for epic bat flips and for being the first professional sports league to resume play following the COVID-19 pandemic. Conventional wisdom says that the caliber of play is roughly Double-A, but that overestimates the league's current capabilities.

By Double-A, most pitchers either have good stuff but struggle with command or decent command of subpar stuff. KBO pitchers averaged 89.1 mph on the radar gun in 2023, roughly five ticks below the MLB average. For every 92 mph fastball, someone is topping out at 86.

Command is harder to quantify, but this author watched KBO games on ESPN during the pandemic and Korea's early morning games during the 2023 World Baseball Classic. Command and control were lacking in these eyes, even for the KBO All-Star team in the WBC.

The KBO's statistics last season suggest nothing's changed. The league hit .277/.352/.420 with a 9 percent BB% and 19 percent K%. The Kia Tigers were the league's runaway champions and led the league with a 4.40 ERA. All 10 teams allowed more than five runs per game.

The lack of pitching means KBO hitters don't face anything resembling big league pitching until they leave Korea, generally facing a lengthy adjustment period. Jung Hoo Lee hit .262/.310/.331 with two homers in 158 PA before an injury derailed his season.

Ha-Seong Kim struggled mightily in his first big league season, slashing a putrid .202/.270/.352 with eight homers and six steals in 298 PA back in 2021. He didn't become a fantasy option until two years later.

Hyeseong Kim couldn't land an MLB job this offseason after hitting .326/.383/.458 with 11 HR and 30 SB in the KBO last season. The Dodgers are a difficult roster to crack, but he presumably would've chosen an MLB role somewhere else if one was offered.

Long-term projects make sense for MLB teams, but fantasy managers should fade KBO imports, considering the expected adjustment period. It's just too big a jump in opposition to expect immediate success.

Projecting Imports from Nippon Professional Baseball (NPB)

Conventional wisdom says the NPB is roughly equivalent to Triple-A, but that underestimates the league. The replacement level is lower than MLB since the league pulls from a smaller player pool, but top-line Japanese players are all MLB-caliber.

Interest in NBP is also extremely high, meaning tools have been developed that are comparable to Baseball Savant. The NPB Pitch Profiler developed by bouno05 is one of the coolest. It has a bare-bones interface, but that just makes it easier to use.

You can ignore most of the boxes. It defaults to last year, but you can toggle to any year since 2020 for more data. When you have the right year, scroll down to "Select or Input a Player" and type in the name you want to look up.

Note that it uses phonetic English spellings, meaning Roki Sasaki isn't in the database, but "Rohki Sasaki" is. Luckily, it is smart enough to give you the name you want most of the time. Click "Generate!" to see a wealth of information.

We'll use Shota Imanaga's 2023 season as an example to see if we can predict his MLB performance with the benefit of hindsight. The default view looks like this:

That's a lot, but we have platoon splits, K%, BB%, GB%, HR/FB, and even SIERA. NPB's league averages are included for context, and the numbers represent percentiles just like Baseball Savant.

Imanaga was in the 99th percentile for K% and 81st for BB%, meaning he dominated in the first two things fantasy managers look at. His MLB marks last year were 25.1 percent K% and 4.0 percent BB%, so the raw Japanese stats were a decent MLB projection.

We also see that Imanaga's GB% was low at 35.3 percent. His MLB mark was 37.2 percent, so again, the raw number was a reasonable projection.

However, we haven't seen the best stuff yet. Click "Pitch Arsenal" below the "Generate!" tab for granular data on every pitch Imanaga threw.

This is Pitch Info. We have SwStr%, GB%, IFFB%, Stuff+, and Location+ among other things. Let's focus on SwStr% and compare his 2023 arsenal to his 2024 Pitch Info data.

The NPB Pitch Tracker classified Imanaga's splitter as a change, and its SwStr% increased at the MLB level. The same is true of his slider and sinker, while his fastball remained respectable against MLB batters. If anything, Imanaga may have deserved more strikeouts than he generated in his rookie season since his SwStr% increased.

We can infer additional information from these statistics, too. Imanaga's fastball combined a low 25 percent GB% with a 17.3 percent IFFB% and elite 125 Stuff+, suggesting a high-spin offering. Sure enough, Imanaga averaged 2,442 RPM on his fastball with 98.8 percent Active Spin last season. He only averaged 91.7 mph on the radar gun, but his fastball had the late life necessary to succeed.

Imanaga's NPB data had a direct correlation with his MLB performance. This will help us project Sasaki, Tomoyuki Sugano, and anyone else who comes over from Japan.

Bouno05 developed an NPB Bat Profiler, too, and the interface is the same. There hasn't been a high-impact Japanese bat in a while, but 3B Munetaka Murakami is expected to be posted after the 2025 season. Here is a preview:

He strikes out too much and hits enough fly balls to hurt his BABIP, but we're looking at big power here. The 25-year-old is also more than willing to take a walk. The downside is probably Rhys Hoskins, with the upside looking like prime Pete Alonso.

Conclusion

Fantasy managers might not be familiar with the tools to evaluate foreign players, but they're out there and will only become more important as more players jump to MLB. Learning them now could give you a competitive advantage for years to come.

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