From the opening two-game series of the Korean professional baseball season, 25 home runs were hit in 10 games, but the coefficient of restitution for KBO official balls has decreased.

The KBO announced the results of the first interim inspection of the 2025 Shinhan SOL Bank KBO League single game ball on the 25th.

This inspection involved randomly collecting five samples of the KBO League single game ball, the Skyline Sports AAK-100, and was conducted by the Korea Sports Promotion Foundation (KSPO) Sports Goods Testing Center from the 21st to the 24th.

The inspection results confirmed that all samples met the passing criteria. On average, the coefficient of restitution was 0.4123, the circumference was 232mm, the weight was 144.12g, and the seam width was 7.03mm.

The most noteworthy aspect is the coefficient of restitution. With an average of 0.4123, it meets the passing criteria of 0.4034 to 0.4234. This figure is a decrease of 0.0026 compared to the coefficient of restitution (0.4149) reported during the second interim inspection of the 2024 game ball on April 30 of last year.

Generally, it is known that an increase in the coefficient of restitution by 0.001 adds about 20cm to the distance. Compared to last year's second inspection value, the decrease of 0.0026 in the coefficient of restitution is theoretically expected to reduce the distance by approximately 50cm, allowing home run balls that barely clear the fence to be caught on the warning track.

The KBO official ball's coefficient of restitution fell to 0.4061 in 2022 but rose to 0.4175 in 2023, and on March 22 last year, it was reported to have increased to 0.4208 during the first inspection. This marks the first return to the 0.42 range in five years since the second inspection in 2019 (0.4252). Although it dropped to 0.4149 in the second inspection, the KBO League continued to experience a hitting-friendly atmosphere.

Last year, the league batting average was .277, ranking sixth among the 42 seasons, the highest ever. The championship team, KIA, had a team batting average of a remarkable .301. With 1,438 home runs, it was the fifth-highest total in history. Among the players on the field, voices expressed concern that 'the balls are flying too well.'

It was a hellish season for pitchers, and this opinion was predominant even from the early exhibition games, claiming that the balls bounced well. In fact, during the opening two-game series, 25 home runs were hit, leading to doubts about the 'year of the bouncy ball' turning into certainty. LG exploded with 7 home runs at the largest stadium in the country, Jamsil Stadium. At the Daegu Samsung Lions Park, known for producing home runs, Samsung hit 6 and Kiwoom 3, with a total of 9 home runs.

In the early part of the season, it is usual for strong pitchers to have an advantage over batters. Considering that this is the opening series featuring each team's top 1-2 starting pitchers, the record of 25 home runs and an average of 11.6 runs per game is an exceptionally high figure.

However, the results of the first inspection of the KBO official ball showed a decrease in the coefficient of restitution compared to last year, and it is also significantly lower compared to the 2023 season, which experienced a hitting-friendly environment. The weight of the ball has decreased from 144.57g in last year's second inspection to 144.12g, a difference of 0.45g, which could also impact the distance. Although the weight has reduced by 2.03g compared to the 2023 hitting-friendly season (146.15g), the fact that home runs poured out during the opening two-game series does not imply a significant relationship with the official ball's coefficient of restitution.

While it could be interpreted as an advancement in hitters' skills or power, the sample size is too small. Only 10 games have been played in the very early stages of a season with a total of 720 games. It is premature to draw a conclusion of 'bouncy ball' based solely on the results of the opening two-game series. It is advisable to accumulate more samples and make judgments after observing the results from the second interim inspection.

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