Tackling is a fundamental defensive move in American football, with the main purpose of stopping the forward motion of the ball-carrier. However, current tackling metrics are manually recorded outcomes that are inherently flawed due to their discrete and subjective nature. Using player tracking data, we present a novel framework for assessing tackling contribution in a continuous and objective manner. Our approach first identifies when a defender is in a ``contact window'' of the ball-carrier during a play, before assigning value to each window and the players involved. This enables us to devise a new metric called fractional tackles, which credits defenders for halting the ball-carrier's forward motion toward the end zone. We demonstrate that fractional tackles overcome the shortcomings of traditional metrics such as tackles and assists, by providing greater variation and measurable information for players lacking recorded statistics like defensive linemen. We view our contribution as a significant step forward in measuring defensive performance in American football and a clear demonstration of the capabilities of player tracking data.

翻译：擒抱是美式橄榄球中防守方的基础动作，其主要目的在于阻止持球者向前推进。然而，当前衡量擒抱表现的指标主要依赖人工记录的结果，因其离散性和主观性而存在固有缺陷。本文提出了一种基于球员追踪数据的新框架，能够以连续且客观的方式评估擒抱贡献。该方法首先在比赛过程中识别防守队员进入持球者“接触窗口”的时机，随后对每个窗口及涉及球员进行价值评估。基于此，我们设计了一种名为“分数擒抱”的新指标，用于量化防守队员在遏制持球者向端区推进方面的贡献。实验证明，相比于传统擒抱和助攻指标，分数擒抱通过为缺乏统计数据（如防守线卫）的球员提供更大的差异性和可量化信息，有效克服了传统指标的局限性。我们认为，这一成果是美式橄榄球防守表现评估领域的重要进展，同时充分展示了球员追踪数据的应用潜力。