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
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.
2025 player ranking guess
Again, the expected value is given in win shares.
Feeling a draft
A related little project I did, examined the first-year value produced by drafted players bases on their overall rank in the NPB draft and whether they are coming out of high school, college, the corporate leagues, independent ball or elsewhere.
Because players coming out of independent ball were very rare until the last couple of seasons, a lot of them had no precedents at their draft rank, in which case I assigned the average first-year value of all players taken at the same rank.
This was important because last year’s draft saw 18 players drafted out of independent ball, seven by the Hanshin Tigers.
