Why the Assistant Referee Was Set an Impossible Task
An assistant referee has to resolve two things that occur in different places at the same time. One is the instant of contact between a teammate's foot and the ball, often behind or beside the assistant. The other is the alignment of attacking and defending bodies along a line running across the pitch. Human vision cannot attend to both at once. The eye has to move, and the moment it moves it loses precise information about what it just left, so the judgment becomes a reconstruction from short-term memory rather than a direct observation.
Vantage point makes it harder. The assistant stands level with the defensive line but off to one side, which means every player is seen at an angle rather than edge-on. A shoulder that reads as being in front from the touchline can be level or behind when viewed from directly above, and the discrepancy grows with distance. Motion adds a further distortion, since a moving object tends to be perceived slightly ahead of where it actually sits at the instant a separate event registers, a bias that is systematic rather than random.
