How can a referee determine if a goal has been scored?

A goal is officially scored when the entire ball crosses the goal line, which is the clear standard established in the Laws of the Game. This requirement ensures that there is no ambiguity about whether a score has been achieved. Referees are trained to observe and confirm that the ball has completely passed over the line, which is a definitive and objective criterion.

While a ball being in the penalty area or players’ reactions can provide context to the play, they are not definitive indicators of a goal being scored. The referee's sole decision without confirmation from the other factors would also not suffice; the actual crossing of the goal line is the definitive action that constitutes a goal. Thus, the proper understanding of how a goal is scored hinges on this clear and measurable action of the ball crossing the goal line completely.