Chang-mo Koo Is Always Ahead

Modern baseball writers are a somewhat spoiled bunch. If you’re writing a story about an MLB player, you have seemingly countless resources at your disposal to gather more statistics than you might know what to do with. For example, say that I wanted to write about Cleveland Indians starting pitcher Shane Bieber. His player page on this site lists any standard or advanced metric I could want, along with info on things like how hard he throws his fastball and how often opponents chase his pitches out of the zone. If I see he struck out 259 batters in 2019, and want to know how many other pitchers in the live ball era struck out at least 250 batters in just their second big league season, I can use Baseball-Reference’s Play Index to find the answer. If I want to get more specific, and learn how many times Bieber struck out a right-handed hitter with a breaking ball out of the zone, Baseball Savant’s search feature has me covered there too.

When it comes to writing about foreign professional leagues, however, the wealth of information isn’t quite so grand for the American writer. Sites like MyKBO.net and Statiz are great resources, and our KBO leaderboards tell us a lot of great stuff — like the fact that NC Dinos left-hander Chang-mo Koo 구창모 leads all pitchers in both ERA and FIP after four starts – but if you want to dig into why or how he’s doing that, we don’t have the pitch-by-pitch data to identify things like velocity, spin rate, or how batters are performing against individual offerings. That hasn’t diminished my curiosity about Koo, though, so I used the tools available to me — Twitch and ESPN archives of game broadcasts, a notepad, and my own two eyes — to track his pitches over his first four starts, in the hope that doing so would reveal something interesting. Fortunately, both for myself and my editor who enjoys for me to have story ideas, it did.

First, some background. Koo, 23, is already in his fifth season pitching in the KBO. The southpaw was used mostly as a reliever in his rookie year, making 38 appearances (including nine starts) and holding a 4.19 ERA in 68.2 innings. He took on more of a starter’s workload in the next two seasons and growing pains abounded, as the young Koo finished the 2017 and ’18 seasons with ERAs of 5.32 and 5.35, respectively. Last year, however, he began to turn a corner. He led all KBO pitchers (min. 100 innings) with a 9.59 K/9 mark, and also set career bests in walk and home run rates en route to a shiny 3.20 ERA.

This season, it seems he’s taken another step forward. His first start of the year, a game against the Samsung Lions that was broadcast on ESPN, was a six-inning shutout performance during which he allowed just two hits and struck out eight. In his next start, he tossed eight shutout innings against the KT Wiz, allowing four hits and striking out 10. After allowing just one run in each of his last two outings, Koo is pacing the KBO in just about every category.

With such dominance across the board, you might expect to turn on a Koo start and very quickly see an explanation for what’s made him so unhittable — an explosive heater, a 70 breaking ball, or even a Yu Darvish-like deep assortment of pitches. Instead, many of Koo’s traits seem somewhat ordinary, even after adjusting your expectations for the stuff KBO pitchers tend to exhibit. His fastball can touch 93, but it tends to stay in the 88-90 mph range — toward the harder side of KBO starters, but not elite, and without much movement. He has a long, loopy curveball that sometimes slows down into eephus territory, which he’ll use sparingly. His biggest weapon, however, is his slider, which he throws in the low-80s and which can completely flummox hitters. It lacks late, hard-breaking movement, instead employing a Patrick Corbin-like shape.

Koo Chang-Mo, Winner by KO. ? pic.twitter.com/DL86bnqueM

— Rob Friedman (@PitchingNinja) May 26, 2020

That slider has done much of the legwork in making Koo one of the best strikeout arms in the league. According to my own tracking, 22% of the sliders he’s thrown have drawn swings and misses, and he uses the slider over 38% of the time. Overall, Koo owns a 13.3% whiff rate, a mark that would have placed him 13th in the majors among qualified starts in 2019, just a tick behind Darvish (13.4%).

In the process of watching all four of Koo’s starts, it wasn’t his swing-and-miss capabilities that stood out most, though – it was his aggressiveness. In his start against the Kiwoom Heroes on Tuesday — a seven-inning, one-run, three-hit performance — he started catcher Ji-young Lee 이지영 off with a fastball out of the zone for ball one to begin the fourth inning. He battled back with two fastballs in a row for strikes, and finished him with a curveball for a strikeout. He then retired the next nine hitters he faced in a row — all without ever falling behind in the count. I noticed a similar run during his start against Doosan, when he fell behind just three of the final 16 hitters he faced. I went through every plate appearance of Koo’s season, and it turns out, those aren’t flukes.

You don’t need me to tell you that hitters perform better when they’re ahead in the count than they do in other situations. Last season, hitters produced a .432 wOBA in what Statcast considers batter-friendly counts (1-0, 2-0, 2-1, 3-0, 3-1 and 3-2), compared with a .313 wOBA in even counts, and a .225 wOBA in pitcher-friendly counts. An 8-year-old in their first year of little league knows the concept of count leverage in their bones, but that doesn’t change the fact that hitter’s counts still happen with more or less the same frequency every year. Since 2008, the percentage of total pitches that occur in hitter’s counts has only ranged from 26.8% to 28.8%.

Even on an individual level, pitchers don’t deviate from this much. In 2019, the league-wide share of pitches in hitter’s counts was 26.9%. The pitcher with a minimum 1,000 pitches thrown and the lowest percentage of pitches happening in such unfriendly counts was Chris Paddack, who clocked in at 19.4%. In fact, if my data is correct, Koo’s hitter’s count percentage would be lower than any recorded MLB pitcher season dating back to 2008.

You might be tempted to write this off at least somewhat as the KBO being different from MLB in terms of how pitchers attack hitters, or vice versa. But I wouldn’t be too sure of that. Remember how narrow the range of MLB’s data for this is, despite the fact that over the past 12 seasons, the run-scoring environments have varied dramatically, and the philosophy of how both hitters and pitchers approach each plate appearance has quickly evolved into something different from anything the game has seen before. If the rate at which batters are in friendly counts has remained in place through all that, I think it’s a good bet that the KBO’s league rate is probably quite close to MLB’s, which would make Koo every bit the outlier he would be in an MLB sample.

Could this change as the year goes on? Of course it could. The season is very young, and with the KBO trying to squeeze as many games as possible into a shorter-than-usual timeframe, fatigue is likely to hinder Koo at some point or other. But seeing a pitcher this young be able to apply this much pressure to hitters so consistently through four starts is worth taking note of. And while more information is always better and makes things more interesting, the truth is it doesn’t take a wide range of numbers to appreciate how great Koo is. You don’t even need a notebook and pen. Simply watching what he does to opposing hitters is enough.

23-year-old Koo Chang-mo (???) continues his stellar start to the season ?

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— taewoongi (??) 16-3 (@taewoongii) May 26, 2020