The 'Study in Japan' That Turned the Tide for Kim Jin-wook and Lee Ui-ri: Why Did Kim Seo-hyun, Who Once Threw a 161 km/h Fireball, Settle for 151 km/h?

*This content was translated by AI.

Kim Seo-hyun (22) of Hanwha Eagles, who made headlines last year for throwing a fastball clocked at a top speed of 161 km/h, expressed satisfaction even with a "slow" pitch of 151 km/h.

Speaking to reporters ahead of the Daejeon LG Twins game on the 21st, Kim Seo-hyun said, "I was very nervous since it had been a while since I stepped onto the first-division mound. It was also my first time showcasing what I prepared in the minor league in actual competition, so I felt a lot of pressure to perform well."

Earlier, on the 20th, during the Daejeon KIA Tigers game, Kim Seo-hyun entered the mound in the bottom of the ninth inning with Hanwha trailing 6-8, one out, and a runner on first base. Over two-thirds of an inning, he threw 22 pitches, allowing two hits, one hit-by-pitch, recording one strikeout, and surrendering one earned run. This marked his first appearance in the first division after 105 days since the May 7 game against Gwangju KIA. He was not yet at his peak form. His fastest fastball reached only 151 km/h.

Despite this, Hanwha manager Kim Kyung-moon offered a positive evaluation. Manager Kim said, "The performance itself wasn't bad. There were no wildly off-target pitches, and the breaking balls were well-controlled," offering words of encouragement.

Kim Seo-hyun also found meaning in similar aspects. He stated, "Unlike before I was sent down to the minor league, my control didn't feel scattered everywhere. Instead of focusing only on my own pitching, I aimed to compete directly with batters. Since the ultimate goal is to engage with batters and produce results, I concentrated on that aspect."

For someone once known for his overpowering fastball exceeding 160 km/h, this represents a significant shift. After graduating from Seoul High School, Kim Seo-hyun was selected as the first overall pick in the first round of the 2023 KBO Rookie Draft and donned the Hanwha uniform. A fast pitch had always been his identity, with his overpowering fastball exceeding 160 km/h being his greatest weapon.

However, there were also many days when his pitching motion became unstable and control faltered as fatigue set in. This season was particularly challenging; in 12 games during the first half, he recorded one win, two losses, one save, and an ERA of 12.38.

The visit to Japan's Next Base Athletic Lab last month with Kwon Min-kyu (20) is one of several breakthrough initiatives provided by Hanwha. The lab has recently gained attention in Korea for offering solutions to pitchers like Kim Jin-wook (24, Lotte Giants) and Lee Ui-ri (24, KIA), who were struggling with similar issues. Over 100 Japanese professional baseball players visit this facility annually. Kim Seo-hyun approached the program with a different starting point.

He carefully examined how his body moves during the pitching process. Kim Seo-hyun explained, "They use measured data to identify areas where pitchers are lacking. By reviewing graphs, they explain how to achieve the most ideal movements possible. The benefit of biomechanical measurement is that it reveals even the parts of the body that aren't functioning well."

A KBO club official who personally toured the facility offered a similar explanation. This official highlighted that the facility's strength lies not in short-term "corrective effects" but in detailed diagnosis. They examine everything from toe movement to joint motion and angles, as well as body stiffness, and use biomechanical analysis to determine where energy is lost during the pitching process.

However, there was caution against assuming that a player would suddenly improve just by visiting an external facility for a few weeks. A KBO club official stated, "It's not about immediate performance improvement in a short period; rather, the value lies in accurately diagnosing what is currently hindering the player's performance."

Kim Seo-hyun did not believe he found all the answers in Japan. Instead, since returning home, he has focused on adapting his pitching mechanics to fit his own style. Making his pitching motion more concise and consistent is part of that process.

His approach differed from Kwon Min-kyu, who traveled with him. Kim Seo-hyun said, "If (Kwon) Min-kyu's goal was to significantly increase speed, I focused on learning pitch design and how to effectively utilize different parts of my body." He added, "Since we learned different things, after practice ended, we often discussed what each of us had learned that day."

Kwon Min-kyu first demonstrated his potential in the Daejeon LG game on the 21st. After starting pitcher Bruce Zimmermann collapsed in one-third of an inning, allowing seven earned runs, Kwon entered as a relief pitcher and held the line for four and a third innings, surrendering only three earned runs. Hanwha overturned a 0-9 deficit in the third inning to win 15-11, ending their six-game losing streak.

For Kim Seo-hyun, the immediate change needed is not "faster" but "more accurate." He stated, "Of course, I want to increase my speed. I've heard that if control becomes stable and confidence grows, velocity will naturally follow. For now, I'm trying not to focus too much on speed."

Instead, he felt relieved upon confirming his 151 km/h fastball. Kim Seo-hyun emphasized, "Still, throwing around 151 km/h means my velocity is acceptable. My priority right now is to maintain stability." He viewed this not as abandoning faster pitches but as rearranging priorities: facing batters, delivering the desired pitch first, and then gradually increasing speed.

Kim Seo-hyun expressed his ambitious goal: "I won't rush things. I'll do what I've prepared for. I want to help the team as much as possible by showing gradual improvement."

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*This content was translated by AI.