What is semi automated offside in football?

Dedicated cameras mounted under the stadium roof sample body points on every player dozens of times per second, building a three-dimensional skeletal model of the pitch. The ball is tracked in parallel, and in some installations a sensor inside the ball reports the exact moment of the kick at very high frequency. Software fuses the two streams, matching the instant of the pass with the attacker's position automatically.

When a player in an offside position moves toward the ball, the system alerts the video operation room. The video officials confirm the kick point and the selected body parts, then inform the referee. After the decision, spectators are shown a three-dimensional animation of the position, replacing disputed hand-drawn lines with a model everyone sees the same way.

The technology was developed as an answer to long VAR offside reviews and the arguments generated by manually drawn lines. FIFA brought the system into service at the 2022 World Cup, and a goal ruled out by automated alert in the very first match of the tournament became its shop window.

Since then the system has been spreading through major continental competitions and top-flight leagues. Which league uses it, and from which season, depends on each organisation's own decision and infrastructure investment; the cost of installation means adoption moves in stages rather than all at once.

The positional measurement is far more precise than manually drawn lines; replacing the human ruler with data is the system's whole reason for existing. Machine-learning techniques help track limbs in the video feeds, but the process is never left entirely to software: the video officials confirm that the kick point was captured correctly and that the right body part was used. The word semi in the name comes from that human layer.

Part of offside can never be reduced to measurement anyway. Whether a player was actively involved, or blocked the goalkeeper's view, requires interpretation and stays with the referee. The system settles the question of position; the question of involvement remains a human call, which is why the technology accelerates officials rather than replacing them.