Former Yomiuri Giants star Warren Cromartie and I had an argument the other day about when ballplayers reach their prime, and since I tend to be a know-it-all, I looked to see what the evidence suggests. After looking to find out who actually has been the best player in Japan since 2020 and when Japanese players reach their peak, it turns out we were both kind of wrong.
Our discussion began with his evaluation of the relative strengths of two players who appear headed for a switch from Japan’s majors to MLB, the Giants’ Kazuma Okamoto and the Yakult Swallows’ Munetaka Murakami.
Former Giants manager Tatsunori Hara put Cromartie in uniform a few years ago so he could help Okamoto find his feet, and boy did the youngster respond.
Okamoto will be 29 on June 30, has played seven full seasons. He is on track to be an international free agent after the 2026 season, and Cromartie said he has reason to believe the Giants will post him this autumn.
Here are some observations about player personnel moves ahead of the 2025 season and some wild predictions, based on a not-very scientific study player growth and aging.
Player growth and aging
A more thorough study would have sought to estimate how many games a player will take part in, since playing time has a huge impact on overall value. But I didn’t go there.
Instead, I took at the value per game and the amount of playing time changed with age for the best pitchers and position players in Japanese baseball history to get aging curves for both quality and playing time.
I then applied these to the average playing time and quality for each player over the previous two seasons, and bingo, bango, bongo, I had an estimated value for each player in 2025. Not scientific, but do-able.
The value is measured in Bill James’ Win Shares, which I’m sure some of you don’t like, but tough. It rates even the best modern pitchers with their 200-inning seasons lower than the best position players, but the logic for that is compelling.
All you really need to know at this stage is that three win shares are equivalent to one team win.
Now let’s start by looking at who are the players leaving their old teams, either joining new ones in Japan, hanging up their spikes or getting out of Dodge and heading to the Dodgers…
The biggest leavers
Leaving
Name
Expected Value
New NPB Team
Marines
Neftali Soto
13.4
Marines
Roki Sasaki
12.4
Dragons
Raidel Martinez
12.0
Giants
Hawks
Takuya Kai
11.4
Giants
Giants
Tomoyuki Sugano
8.1
Lions
Albert Abreu
6.5
Tigers
Sheldon Neuse
6.0
Marines
Cristopher Mercedes
5.8
Hawks
Masaki Mori
5.7
BayStars
Hawks
Tsuyoshi Wada
5.7
Leaving
Name
Expected Value
New NPB Team
The first thing to notice here is that the Marines really took some hits over the winter, losing three of the highest-value leavers in Neftali Soto, Roki Sasaki and CC Mercedes, while the Giants scooped up two of the top 10, catcher Takuya Kai and closer Raidel Martinez. Unfortunately, the Giants can’t play all four of their top catchers at once, but they’ll figure something out.
Below are the projected 2025 season values of every player with NPB experience.
