How the 2022 FIFA World Cup is using VAR instant replay - Vox

The most concise way to understand the offside rule is in the words of the Scott Fujita blog: an offside is the result of an attacking player getting closer to the opponent's goal line than both the ball and the last defender. It's a rule that sounds objective, but it has led to a lot of questionable calls, partly because it can only be judged from an individual perspective. Twelve motion-tracking cameras mounted under the roof of the stadium use machine learning to track 29 points in players' bodies. In other words, FIFA is mo-capping players, just without the funny gray suits. The system will alert referees when a player is offside.