Despite appearing in only 113 games, he remained in contention for the Home Run title until the final game of the season.

Chiba Lotte Marines player Koki Yamaguchi hit 38 Home Runs this season, showing a great performance that kept the possibility of a title alive until the final game of the season. Despite appearing in only 113 games, the fact that he was only two behind Ryoya Kurihara, who won the Home Run king title, speaks to the uniqueness of Yamaguchi's performance this season.

This time, we will introduce in detail the areas where Yamaguchi has grown this season, based on various indicators he has recorded so far. In addition, by checking the monthly results recorded by Yamaguchi, we would like to look back once again at the overwhelming performance he showed from May onwards.

Not only with Home Runs, but his clutch performance also shines with the 4th most RBIs in the league and four walk-off hits during the year.

The annual metrics recorded by Yamaguchi during his time with the first team are as follows.

After making his first-team debut in 2021, his third year out of high school, and hitting 9 Home Runs, he recorded 16 Home Runs in 102 games the following year in 2022. In 2023, he reached the required number of plate appearances for the first time and steadily built his career with 14 Home Runs, but in 2024, his number of games played decreased to 51, less than half of the previous year, and he struggled with a slump, hitting only 2 Home Runs.

In the following year, 2025, although his opportunities further decreased to a career-low 35 games, he achieved the feat of hitting Home Runs in four consecutive plate appearances from August 19th to 21st. He left an impact in limited plate appearances, recording 7 Home Runs and 24 RBIs in just 112 plate appearances.

Then, in 2026, he made rapid progress by hitting 38 Home Runs, more than double his previous career high from 2022. He broke the club record for the most Home Runs since the move to Chiba, which was 35 set by Benny Agbayani in 2004, and delivered a masterpiece performance that etched his name in club history amidst a continuing trend of pitcher-dominated baseball.

In addition to repeatedly drawing spectacular arcs, Yamaguchi's clutch hitting was also outstanding this season. While he was often entrusted with the 1st or 2nd spot in the batting order toward the end of the season, he recorded 81 RBIs, ranking 4th in the league, and contributed greatly as a point-getter, including hitting four walk-off hits during the year. He responded to the aggressive batting order usage that is a trend in modern baseball and literally played the role of powerfully leading the lineup.

He recorded figures that topped the league across the board in indicators related to extra-base hits.

The degree of growth shown by Yamaguchi this season is also reflected in the numbers. His slugging percentage this season is .602, significantly exceeding his career average of .441. Furthermore, his "ISO," which is described as the "true slugging percentage" by removing the influence of single hits from the slugging percentage, stands at a league-leading .325, an outstanding level that shows no one could match him in terms of long-distance hitting power.

Regarding "AB/HR," which indicates the number of At Bats required to hit one home run, he recorded a league-best and stunning 10.84. The AB/HR of Kurihara, who won the Home Run title, was 13.48, which is an excellent figure surpassing Reyes' number from the previous year (14.88). Therefore, Yamaguchi's figure, producing home runs at a pace more than 2.5 plate appearances faster than Kurihara, is particularly noteworthy.

Looking at indicators related to plate discipline, his "IsoD," which shows the difference between batting average and on-base percentage, stands at a somewhat low career total of 0.62. His "BB/K," calculated by dividing Walks by times struck out, remains at a level that cannot be called high at .307. Especially since 2024, both IsoD and BB/K have been modest, indicating that he has adopted an aggressive hitting style in recent years.

This trend has not changed in this breakthrough season, with an IsoD of .052 and a BB/K of .252, continuing a batting style of hitting strikes aggressively. On the other hand, his batting average reached a career-high .277, showing a significant improvement in consistency. Along with this, his on-base percentage reached a career-best .329.

With the dramatic rise in slugging percentage and the improvement in on-base percentage combined, his OPS reached .931, greatly exceeding his career average (.743). Recording the third-highest figure among those who reached the regulation number of plate appearances, following Kensuke Kondo and Reyes, demonstrates that Yamaguchi exhibited league-leading productivity this season.

Regarding "BABIP," which indicates the ratio of balls in play (excluding home runs) that became hits, his career average is .272, significantly below the general standard of .300. Since BABIP is considered an indicator easily influenced by luck, it suggests that Yamaguchi has had aspects of being unlucky throughout his career.

As a right-handed hitter with a style of swinging the bat powerfully, Yamaguchi tends to have few infield hits, and it is necessary to consider that balls that become home runs are not included in the BABIP calculation. However, despite this season's BABIP being .283, which is below the standard, the fact that he recorded career highs not only in home runs but also in batting average speaks volumes about Yamaguchi's significant growth as a hitter.

Despite struggling through April with 0 Home Runs and a .077 batting average, they displayed phenomenal hitting power from May onwards.

Next, let's take a look at the monthly performance recorded by Yamaguchi this season.

In March, he had 0 hits in 2 At Bats, and in April, he managed only 1 hit in 6 games, failing to produce results in the early stages. By the end of April, he was struggling with 0 Home Runs and a .077 batting average. However, starting with a brilliant performance in May where he recorded 6 Home Runs and a .967 OPS in 17 games, he went on to record constant figures of 5 or more Home Runs for six consecutive months. He mass-produced arches at a truly phenomenal pace, hitting 38 Home Runs from May onwards alone.

Furthermore, regarding OPS, he maintained extremely excellent results of .800 or higher for six consecutive months from May onwards, including .960 or higher in five of those months excluding September. In addition to continuing to hit Home Runs, the fact that he maintained superior productivity as a hitter until the very end from May onwards is an element that cannot be overlooked.

In particular, in August, he mass-produced Home Runs at a terrific pace with 10 Home Runs in the month, showing an outstanding performance with a .302 batting average and .979 OPS to win his first monthly MVP. Furthermore, in October, he displayed an overwhelming hitting stroke that surpassed August, with 5 Home Runs, a .308 batting average, an .885 slugging percentage, and a 1.218 OPS in just 6 games, making a fierce charge at the very end of the season to liven up the Home Run king race until the very last moment.

Will they be able to secure the batting title they missed out on this season in the next one?

The Chiba Lotte Marines' team Home Run count increased dramatically from 73 last season to 131 this season, and it goes without saying that Yamaguchi's great performance contributed significantly to this dramatic increase in Home Runs. For a team that had been suffering from a chronic shortage of Japanese sluggers, it is no exaggeration to say that the rapid progress Yamaguchi made this season is significant enough to change the team's culture. Even with a high number of At Bat, his consistency remained impressive.

Since he is 26 years old and still has plenty of room for growth, the fact that further evolution can be expected in the future is also a bright spot. Will the finally born Japanese-made cannon of Makuhari continue to fight as the main gun from next season onwards and win the individual titles he missed by a narrow margin? If he can perform throughout the full season as he did from May onwards, the possibility of that should naturally increase.

Text by Ryota Mochizuki