The KBO is not known for producing power pitchers. The top pitchers that the KBO has exported to North America recently can be classified as control pitchers who lack power. Hyun-jin Ryu, Kwang-hyun Kim, Josh Lindblom, and Chris Flexen are not at the top of anyone’s list of power arms.

However, one KBO pitcher is breaking that mold by becoming a homegrown Korean power arm. Woo-jin An of the Kiwoom Heroes is the KBO’s version of Jacob deGrom, a flamethrower who also has a feel for pitching, and whose starts are must-see events (though we’re not saying they are comparable skills-wise).

If we were going to compare him to a current MLB pitcher, we’d say he somewhat resembles the good version of Rockies pitcher Germán Márquez in that they throw fastballs at similar velocities and throw a hard breaking ball.

An will likely become eligible to be posted after the 2024 season, but he’s worth taking a closer look at now, during the KBO All-Star Break. He currently has a 2.02 ERA and an 0.96 WHIP, and is averaging 10.1 strikeouts per 9 innings.

An has the build of a traditional starter, though he is a bit lean, listed at 6’4” and 202 lbs. At 22 years old, he could add some muscle to his frame if desired.

His bread-and-butter are his fastball and slider. And he throws both hard, relative to the rest of the league.

While he uses these pitches frequently, he has incorporated his other pitches (a curveball and changeup) more frequently over the last few years. He threw the fastball and slider a combined 83% of the time in 2020 when pitching out of the bullpen, but is down to 73% so far this year.

Woo-jin An 2022 Pitch Usage
Pitch Type Avg. Velocity (MPH) Pitch Usage
Fastball 95 45%
Slider 89<< 28%
Curveball 81 18%
Changeup 84 9%

>> Average slider velocity is same as KBO average fastball velocity

 While his fastball averages 95, An will take some velocity off it in obvious bunt situations to save his arm and get the free out, similar to what Zack Greinke will do in similar situations. When throwing at max effort, An’s fastball will sit around 95-97 MPH, with the ability to touch triple digits. He throws the hardest fastball in the KBO, as LG Twins closer Woo-suk Go is the only other pitcher who averages 95 MPH.

An’s slider is a great weapon, as its average velocity of 89 MPH is right around the league average fastball velocity. Since he throws it so hard, it usually does not get a lot of downward break, and can look more like a cutter at times. Despite that, he does not use it to try to jam left handed hitters, but when he throws it to lefties he usually tries to use it more as a backfoot slider.

He uses the slider vs right handers about as often as he uses his fastball. It’s his go-to strikeout pitch. Right-handed hitters as a whole are whiffing on 44% of their swings vs his slider. In MLB, that miss rate by right-handed hitters would rank in the 83rd percentile for pitchers this season (we’re not saying he’d duplicate that for MLB, just pointing out how impressive it would be).

In the last couple of years An has made an effort to improve his curveball and changeup, and those are showing encouraging results. His curveball has a good, downward action  and, like his fastball, he can vary speeds on it. He has a slower version that he can throw around 75 MPH to try to steal a strike early in an at-bat, but he also can reach back for a harder mid 80s breaker when looking for a strikeout.

Having a strong fastball/slider combo at high velocity helps make his curveball more effective. Batters are hitting only .119 vs the curveball this season, and are whiffing on 34% of their swings. An MLB pitcher with that opponents’ batting average against the pitch would rank among the 10 lowest. 

An’s changeup has been a work in progress, but that work is paying off this year. He has already thrown more changeups this season than he did in the previous two seasons combined, and is his best swing and miss pitch, with hitters whiffing on 47% of swings. In MLB, a pitcher with a similar rate is Devin Williams of the Brewers, who has one of the best changeups in the game.

His changeup does not feature a lot of drop, but it will show good fade sometimes. The key to his changeup’s success is how slow he can throw it. He averages an 11-MPH velocity differential between his fastball and changeup, and with hitters gearing up to hit high velocity they end up way out in front when he throws a changeup.

An uses the changeup almost exclusively to left handed hitters, as he has only thrown 9 changeups to right handed hitters this season. 17% of his pitches to lefties have been changeups, with the usage jumping to 30% with two strikes. He has struck out 21 left handed hitters with the changeup so far, which is more than the 13 total changeups he threw in the 2020 season.

An looks like a future major league pitcher, and at 22 years old he is still fine-tuning his craft. If you had to drop a current KBO pitcher into a MLB rotation today, the best options would be Kwang-hyun Kim (who spent the last two seasons in St. Louis) or An.  

His MLB prospects also look encouraging as his team has had a tendency to allow their players to be posted. Players such as Ha-seong Kim, Byung-ho Park, and Jung-ho Kang were all Heroes before being posted. Hopefully we’ll get to see him down the road.