The Developmental Player System (育成選手制度, Ikusei Sensyu Seido) is a system that allows players to be held for the purpose of training players separately from the 70 registered players under control of each team created in the fall of 2005 at Nippon Professional Baseball (NPB).^[1] It is akin to the practice squads seen in other sports.

The system was established in 2005 to create an environment in which amateur players could gain playing experience after company-owned amateur baseball teams were folding following the economic recession of the Lost Decades.^[2] Players who are part of the system are considered "semi-controlled" in that they play for the team they are signed to but they are not a controlled player and thus their team doe not have exclusive rights to them.^[3]

The Developmental Player System include players drafted as rookies (e.g. Yusuke Kosai, Michitaka Nishiyama), foreign players signed as developmental players (e.g., Raidel Martínez, Liván Moinelo), players drafted as registered players under control but re-signed with a team as developmental players due to their abilities (e.g., Kenta Kurose), players who became free agents with their former team and signed with another team (e.g., Masaru Nakamura, Kouya Fujii), and players who were removed from the registration of players under control and re-signed as a developmental player as an injury rehabilitation assignment (e.g., Takuya Kuwahara, Hiroya Shimamoto). There is an argument that de-registering players who cannot play due to injury and re-signing them as developmental players will protect their careers; on the other hand, the use of the developmental players system, instead of systems like the Major League Baseball (MLB) Injured list, is criticized as contrary to the original intent of this system to develop and provide opportunities to amateur players.^[4] The oldest player to become a developmental player is Soichi Fujita, who signed in 2011 at the age of 39. The longest period as a developmental player was Kousuke Naruse [jp]'s eight seasons (2011-2018) as of the 2022 season.

Player Rules

• Developmental players are not allowed to participate in official NPB games. However, up to five players per team per game are allowed to play in the Eastern League and Western League, the NPB's minor leagues.^[1] These minor league farm teams are considered a team's second squad. If a team as a large amount of developmental and minor league players, they may form a third squad and play in games against independent league teams (such as the Shikoku Island League Plus and Baseball Challenge League), corporate amateur teams, or university teams.^[5][6] The Fukuoka SoftBank Hawks's third squad plays more than 100 games a year.^[7] While there is a difference in contract between a registered players under control and a developmental players, unlike the relationship between players Major League Baseball and Minor League Baseball in North America, all NPB are players on the same team regardless of which squad they are on, and use the same practice facility and player dormitory.^[8]
• A Developmental Player System contract is for a maximum of three years. After this contract expires, the player can become a free agent once and sign with the same team again for a one year extension.^[1] After the fourth season, and each subsequent season, the NPB will announce the player's free agent status.^[9] This measure is intended to increase the player's chances of signing a registration of players under control contract, and during the free agent period, he can negotiate with other teams. For example, in 2019, Hiroki Hasegawa moved from the Fukuoka Softbank Hawks to the Tokyo Yakult Swallows.^[10] A one-year contract is also possible for a registered players under control to re-sign as a developmental player after a free agent announcement has been made.^[3] Players who have not been under contract for three seasons will be placed on the roster of pending developmental players, and other teams will not be able to negotiate with them.^[11]
• The minimum salary is ¥2.4 million and ¥3 million is paid as a preparation fee when drafted.^[1] However, since there is no cap on annual salary, some teams sign players at higher salaries, and players who are re-signed as developmental players from a registered players under control often maintain the salary level of a registered players under control.^[12][13]
• A developmental player's uniform number will be a three-digit number (e.g. 001, 101, or 201) in the numbers of other players and staff being one- or two-digits.

Regulations for teams that own developmental players

• The deadline for re-signing a developmental player to a registered player under control contract is from the end of the season to July 31st during the following season. However, teams are not permitted to change a player's contract status from a registered under control to developmental during the season.^[1]
• Developmental players can only be owned by teams with at least 65 controlled players on their roster by July 31 each eason, and teams with fewer than 65 controlled players cannot own them. However, if a team reports to the Executive Committee that it has re-signed a developmental player as a controlled player or acquired a new controlled player to bring the number of controlled players to 65 or more, and if this is approved, the team may retain the developmental player.^[3] There is no limit to the number of developmental players owned and how many a team has depends on the team's policy.^[14] For example, the Yomiuri Giants and Fukuoka SoftBank Hawks often have more than 30 developmental players, enough to field a third-level squad; conversely, the Hanshin Tigers tend to have only a few players.^[15][16][17] The Fukuoka SoftBank Hawks selected 14 new developmental players in the 2022 draft to implement a four-team system starting in the 2023 season.^[18]

Developmental Players Draft Meeting

• If the total number of players selected at the end of the Rookie Player Selection Conference has not reached 120, a Developmental Players Selection Meeting will be held with the participation of the teams that wish to participate.^[19]

Developmental players trade

• Article 11 of the Nippon Professional Baseball Developed Player Regulations states that a trade of a developmental player held by July 31 is allowed, but as of the 2022 season, there are no examples of such a trade.^[3]

The developmental player system, which began in the 2005 season, has been successful in producing major players for each team (e.g. Yoshiki Sunada, Yuji Nishino). The Yomiuri Giants, who have been heavily utilizing this system since the beginning, have signed more than 50 developmental players as their registered players under control as of the 2022 season. The Fukuoka Softbank Hawks have also signed 40 developmental players as their registered players under control, and have produced players like Kodai Senga and Takuya Kai who have won league titles and awards and represented Japanese baseball on the national baseball team.^[20] The Hokkaido Nippon-Ham Fighters, which had been reluctant to acquire developmental players, drafted a player as a developmental player for the first time in the 2018 draft.^[21] In the 2022 draft, 51 players will be selected as developmental players, the largest number in history, and the acquisition of developmental players is a growing trend.^[22]

• Nippon Professional Baseball
• List of current Nippon Professional Baseball team rosters
• Registration of players under control
• List of developmental players for the Nippon Professional Baseball (at Japanese-language Wikipedia)

• Nippon Professional Baseball Agreement・Unified contract documents - Japan Professional Baseball Players Association Official site (in Japanese)
• Nippon Professional Baseball public notice 2023 - NPB.jp (in Japanese)
• Teams index - NPB.jp