League rules
NPB Roster Rules Explained - First-Team Registration, the 10-Day Rule and Special Exceptions
Nippon Professional Baseball publishes a daily list of roster moves, known as kōji (official announcements), showing which players have been added to or removed from each first team. It looks similar to Korea’s KBO, but there is an important difference: NPB has no separate injured list like MLB or the KBO. Instead it relies on the basic registration rules plus a handful of special exceptions (tokurei). This guide explains how NPB first-team registration works, when a removed player can return, and what the exceptions are.
Two layers: registration and the bench
An NPB first team works on two levels:
- Active registration (shutsujō senshu tōroku): the list of players eligible to appear in first-team games, roughly what other leagues would call the active roster.
- The bench (bench-iri): the players from that list who actually dress for a particular game. The bench can be changed from game to game.
That is why Japanese starting pitchers often sit out of the bench on days they are not pitching: they stay registered but are left off that day’s bench list. Removing a player from the registration altogether is called tōroku massho (deregistration), and that is where the 10-day rule below comes in.
How many players can be registered?
The limits have changed a few times.
| Period | Registered | Bench | Foreign players |
|---|---|---|---|
| Up to 2018 | 28 | 25 | 4 registered (max 3 pitchers, max 3 position players) |
| From 2019 (Baseball Agreement) | 29 | 25 | 4 registered (max 3 pitchers, max 3 position players) |
| 2020 special measures | 31 | 26 | 5 registered, 4 on the bench |
From 2019 the registration limit rose from 28 to 29. In 2020, with the COVID-19 pandemic compressing the schedule, NPB adopted special measures for that season: 31 registered players and 26 on the bench, with up to five foreign players registered but only four on the bench. These special figures are reported to have continued in later seasons, with summaries describing them as still applying in 2024. Because NPB decides each year whether to keep the special measures, check the official announcement for the season you are following.
Foreign players are capped at any one time. Under the standard rule, a club cannot register four foreign pitchers or four foreign position players; each group is capped at three. Clubs with several foreign players therefore rotate them on and off the roster depending on the opponent or the pitching rotation, so a foreign player being deregistered does not necessarily mean he is hurt.
The 10-day rule after deregistration
A player removed from the first-team registration cannot be registered again until ten days have passed. NPB’s official announcements add a note next to each removed player stating the date from which he can be re-registered. For example, a player removed on 19 May cannot return before 29 May.
This creates the same dilemma seen in Korea: deregister a player with a minor knock and lose him for at least ten days, or keep him registered and leave him off the bench for a few games. Because leaving a player off the bench avoids the 10-day wait, it is fairly common in Japan for a player to stay registered but miss several games in a row, which in practice often means a minor injury.
Since NPB has no injured list, even long-term injured players are normally handled through ordinary deregistration. A Japanese report that a player was “removed due to injury” therefore tells you nothing about how long he will be out on its own; you need the club’s diagnosis for that.
The reverse is also true: a removal does not always mean an injury. Japanese clubs often deregister a starting pitcher the day after he pitches and register him again ten days later in time for his next start, using the freed place for an extra reliever or position player in between. When you see a removal in the announcements, check whether the player has just made a start and whether the club has said anything about an injury, since the reason is usually not stated in the announcement itself.
The concussion exception
NPB has operated a concussion exception since 2016. It is designed to stop clubs keeping a player with a possible concussion on the roster just to avoid the 10-day wait.
- A player removed under the concussion exception can be re-registered before ten days have passed.
- The club can call up a designated replacement player, and that replacement can also be re-registered without waiting ten days.
- The original player must complete a set return programme before coming back.
When an announcement lists a removal under the concussion exception, it usually means the player can return relatively quickly once he is cleared. If symptoms persist, though, he may end up missing much longer.
COVID-era exceptions
In 2020 NPB created an infection-prevention exception for that season. If a player or a family member showed possible symptoms or felt unwell, the club could apply special registration and deregistration rules, and a player who tested negative could return within ten days. The system continued in later seasons under new names such as “Special Exception 2021” and “Special Exception 2022”, and replacement players called up under it could also be re-registered without waiting ten days.
These infection-related exceptions were temporary measures built for the pandemic period. Whether anything similar applies in a given season depends on NPB’s announcements for that year.
On Daily IL
Daily IL sorts players into seven statuses: OUT, DOUBTFUL, QUESTIONABLE, PROBABLE, IL (injured list), SUSPENDED and RETURNED. Because NPB has no official injured list, a player deregistered because of an injury is generally shown as OUT, while a player who is still registered but has been missing from the bench with an injury is shown as DOUBTFUL or QUESTIONABLE. When the player is registered again, the status becomes RETURNED. Adding ten days to the removal date gives the earliest possible return. Each status is explained on the status guide page.
Sources
- Daily Sports – NPB first-team registration expanded to 29 (December 2018, Japanese)
- Baseball Channel – NPB announces 2020 special measures (Japanese)
- NPB official – 2020 special measures announcement (Japanese)
- Sportiva – Explaining foreign player registration rules, 2019 (Japanese)
- Wikipedia – Nippon Professional Baseball rosters
- NPB official – Example roster announcement (Japanese)
- Baseball Channel – Roster moves under the concussion exception (Japanese)
- Baseball King – Concussion exception report (Japanese)
Rules can change from season to season and between competitions, so always check the latest official announcements from each league or competition.