The Second Measurement: Turning Players Into Skeletons
The positional half of the problem is solved by reducing each player to a set of tracked landmarks corresponding to joints and body extremities, then reconstructing a three-dimensional skeleton from multiple synchronised camera views. That skeleton is what gets compared, not the outline of a shirt, and the distinction is legally important. Only the parts with which a player could lawfully score count, so a trailing arm is disregarded while a shoulder, a knee or the front of a boot can decide the outcome.
The hard cases are occlusion and physical contact. When two players overlap from the perspective of most cameras, or when a defender's leg passes across an attacker's, some landmarks are hidden and have to be inferred from the geometry of the visible skeleton and from preceding frames. That inference carries uncertainty, and the uncertainty is largest in exactly the crowded penalty-area situations where offside decisions matter most. Automation narrows the error relative to human observation without abolishing it.
