Estimating ballpark effects and team defense in baseball is challenging because batted-ball outcomes are influenced by multiple factors, including contact quality, ballpark environment, defensive performance, and random variation. In this study, we propose a simple and interpretable framework based on Total Bases Residuals (TBR). Using Statcast data from 2015 to 2024, we construct expected total bases conditional on exit velocity and launch angle, and define residuals relative to this baseline. These residuals allow us to separate the effects of ballpark environment and team defense and to estimate them simultaneously within a unified regression framework. Our results show that, when our estimates differ from official MLB metrics, the differences can be explained by consistent patterns in home and away performance for both teams and their opponents, providing empirical support for our approach. Similar patterns are also observed in comparisons with existing defensive metrics. The results also suggest changes in league-wide outcomes and are broadly consistent with developments in the game, including the increased use of data-driven positioning, the restriction on defensive shifts, and possible changes in the physical properties of the baseball. We further introduce a standardized index that facilitates comparison across teams, ballparks, and seasons by expressing effects in units of standard deviation.

翻译：估计棒球场地效应和团队防守颇具挑战性，因为击球结果受多种因素影响，包括击球质量、场地环境、防守表现和随机变异。本研究提出一个基于总垒打残差（Total Bases Residuals, TBR）的简洁且可解释的框架。利用2015至2024年的Statcast数据，我们构建了基于出球速度和出球角度的条件期望总垒打数，并定义了相对于该基线的残差。这些残差使我们能够分离场地环境和团队防守的影响，并在统一的回归框架中同时估计它们。结果表明，当我们的估计值与官方MLB指标存在差异时，这些差异可以通过球队及对手在主场和客场表现中的一致模式得到解释，从而为我们的方法提供了经验支持。在与现有防守指标的对比中也观察到类似模式。结果还表明联盟整体结果发生了变化，并与比赛的发展大体一致，包括数据驱动防守布局的增多、防守布阵的限制以及棒球物理属性可能发生的变化。我们进一步引入了一个标准化指数，通过以标准差单位表示效应，便于跨球队、场地和赛季进行比较。