AI 中文总结
研究2026年世界杯补水暂停是否改变比赛势头，采用比赛内病例交叉设计，发现暂停未改变占优方势头衰减速率，但消除了其停赛时的压力，平均效应小且不同比赛状态下有差异，结果需重复验证。
AI 中文摘要
2026年国际足联世界杯是首个规定补水暂停的赛事，即在每场比赛的上下半场第22分钟左右有短暂停赛，无论天气如何。一种普遍说法是，这些暂停会削弱占优一方的势头。我们采用比赛内病例交叉设计进行检验，将同一场比赛的非暂停分钟作为自身匹配对照。这消除了每个比赛层面的特征，仅根据比赛时间、比分和暂停前的势头状态进行调整。结果表明，暂停后明显的势头减弱并非由暂停导致。无论是否有暂停，占优一方的势头衰减速率基本相同，所以势头在停赛期间恢复，就好像比赛继续进行一样。暂停消除的是该方在停赛分钟内的持续施压，而这在净预期进球中没有留下痕迹。我们将目标定义为对已处理的、局部于观察到的暂停分钟的病例交叉效应。平均效应识别较弱，基于向无未处理分钟窗口的时间趋势外推，而按协变量的交互作用是稳定的。平均效应本身较小且接近零。然而，由于只有99场比赛，该设计缺乏拒绝小效应的能力，所以我们根据效应大小和相容区间而非统计显著性来解读结果。估计值在不同比赛状态下并不一致：对于实力平均且大幅领先的一方，隐含效应是势头损失（在暂停前约+20的水平上接近-4分）。我们将这种状态依赖信号作为探索性结果报告，需要重复验证。
英文摘要
The 2026 FIFA World Cup was the first to mandate hydration breaks, brief stoppages near the twenty-second minute of each half, in every match regardless of weather. A widespread claim holds that these breaks blunt the momentum of whichever side is dominant. We test the claim with a within-match case-crossover design, using non-break minutes of the same match as self-matched controls. This differences out every match-level characteristic and adjusts only for game time, scoreline, and pre-break momentum state. The apparent post-break fade is not caused by the break: the dominant side's momentum decays at essentially the same rate whether or not a break occurs, reverting through the stoppage as if play had continued. What the break removes instead is the continuation of that side's pressure during the stopped minutes, and this leaves no trace in net expected goals. The average effect is only weakly identified, resting on a trend extrapolation into a window with no untreated minutes, whereas break-by-covariate interactions are stable; that average is small and near zero. With only 99 matches the design lacks power to reject a small effect, so we read the results by effect size and confidence interval. The estimates are not uniform across match states. The clearest modifier is team strength: the break effect shifts by about +1.6 momentum points per 100 Elo points of rating advantage, favouring a stronger in-form side over a weaker side that is momentarily dominant, and it is the only statistically significant interaction. A weaker pattern appears by scoreline, where a comfortably-leading side of average strength shows an implied loss near -4 points on a pre-break level of about +20. We report these state-dependent signals as exploratory and in need of replication.
Comments23 pages, 6 figures, 5 tables. Code and data: https://github.com/Ddey07/wc2026-hydration-momentum
