How Rain Delays Affect Games
NPB sees roughly 30-40 games affected by rain each season, concentrated during the June-July rainy season. In 2023, outdoor stadiums experienced 18 rainouts, 14 games resumed after rain delays, and 5 called games due to rain. A rain delay is not merely a pause but a tactical inflection point that disrupts pitcher rhythm, batter concentration, and field conditions. Analysis of the past decade of NPB data shows that in games resumed after delays of 30 minutes or more, the team leading before the delay won 68.4% of the time, roughly 4 points lower than the typical win rate at equivalent leads (about 72%). The primary factor is the forced transition from starter to bullpen during the interruption.
Find books about Rain Delay Tactics on Amazon
Historic Examples - Games Changed by Rain
NPB history is filled with games decisively altered by weather. The legendary October 8, 1994 final-day showdown between Chunichi and Yomiuri saw pre-game rain soften the field, contributing to Giants pitcher Hiromi Makihara's struggles with footing. In Game 5 of the 2007 Japan Series between Chunichi and Nippon-Ham, a 2-hour 17-minute delay forced Nippon-Ham's Yu Darvish out of the game despite his dominant pre-delay performance, a turning point many analysts credit with shifting the series. The 1974 Japan Series between Hankyu and Lotte saw rain postponements break Lotte's momentum, enabling Hankyu's comeback championship. These cases demonstrate that weather can override talent differentials in determining outcomes.
Modern Tactical Responses and Domed Stadium Impact
Six of NPB's 12 teams play in domed stadiums, creating a structural strategic divide regarding rain risk. Outdoor teams like Hanshin (Koshien), Hiroshima (Mazda Stadium), and Yokohama (Yokohama Stadium) must account for rainy-season schedule buffers and deeper bullpen construction. During rain delays, managers face the critical decision of whether to change pitchers before or after the interruption. A 2022 study found that teams making pitching changes before the delay allowed 2.8 runs per 9 innings after resumption, compared to 3.9 runs per 9 innings when the same pitcher continued, suggesting proactive substitution is advantageous. Additionally, breaking ball command deteriorates in wet conditions, with slider batting average against rising from .221 in clear weather to .258 in rain. MLB expanded suspended game rules from 2020, while NPB primarily uses rain-shortened called games - this institutional difference also affects tactical approaches.
Related books are also helpful
Future Outlook
Increasing guerrilla rainstorms linked to climate change pose new challenges for NPB operations. In August 2023 alone, 7 outdoor games were rained out, creating scheduling congestion. NPB began piloting AI-powered weather prediction for game-start decisions in 2024, incorporating rain cloud movement speed and precipitation volume forecasts beyond simple probability percentages. Retractable roof installations are also under discussion, with the planned renovation of ES CON Field Hokkaido in 2025 drawing attention. However, some argue that rain delays and called games embody baseball's inherent uncertainty, and eliminating them entirely could diminish the sport's appeal. Building systems that coexist with weather while ensuring competitive fairness will be a key theme in NPB's future operations.