Rules & Systems

Articles recording the history of rule changes and system reforms

NPB's Double Motion Rule - The Evolution and Controversy of Pitching Form Regulations

NPB has long regulated pitching motions branded as 'double motion,' a topic of debate for over 30 years involving phases of stricter and looser enforcement. The rule aims to prevent unnatural deceptive deliveries but has wrestled with ambiguous adjudication and conflicts with international standards. The 2006 tightening and the 2011 liberalization marked major turning points. We trace the history of NPB pitching-motion regulation through controversy and globalization.

Rules & Systems Estimated reading time: 2 min

Evolution of NPB Roster Limits - How the Expansion from 25 to 31 Active Players Reshaped Lineup Tactics

NPB's active roster has long operated under a 28-player registration cap (with 25 players permitted to dress for a game). After the 2020 COVID-19 pandemic prompted balancing infection control with game operation, the cap expanded, and a 31-player roster has now taken hold. This evolution has reshaped bench tactics, the deployment of development-contract players, and the interplay with the farm system. We trace NPB's roster history from the regulatory side.

Rules & Systems Estimated reading time: 2 min