Goal-Line Technology Explained: How Football Knows the Ball Crossed the Line
For a goal to count, the whole of the ball must cross the whole of the goal line between the posts and under the crossbar. When a shot bounces down off the bar or a defender clears it on the line, the human eye can struggle. Goal-line technology (GLT) answers that question automatically.
How it works
The most widely used systems rely on high-speed cameras placed around the stadium, several pointed at each goal. Software tracks the ball's position in three dimensions many times per second. When the entire ball passes over the line inside the goal frame, the system sends an encrypted signal to the referee.
The referee wears a special watch that vibrates and displays "GOAL". According to the requirements set by football's lawmakers, the signal must reach the officials within one second. Some match officials' assistants also receive the signal through their equipment.
Why it was introduced
Several high-profile mistakes in major tournaments, including clear goals that were not given, increased pressure to use technology. The International Football Association Board (IFAB) approved goal-line technology in 2012. It was used at FIFA's Club World Cup that year, at the 2014 World Cup, and in top European leagues from the following seasons.
Testing and certification
Every installation must pass strict tests before use, and the system is checked before each match. The referee carries out checks with the provider, often by placing the ball on and over the line to confirm the watch responds correctly. If the system fails, the referee decides as before, without technology.
Goal-line technology vs VAR
- GLT answers one factual question: did the whole ball cross the line? It is automatic and nearly instant.
- VAR reviews many types of decisions, including fouls, offside and red cards, and involves human judgement. Read VAR explained.
Even in matches with VAR, the goal-line decision normally comes from GLT. VAR can still check whether an offence happened earlier in the attack.
Where it is used
GLT is expensive to install, so it is mostly found in top professional leagues and major tournaments. Lower leagues and many domestic cup matches at smaller grounds are played without it, which is why goal-line controversies still occasionally happen there.
Common misunderstandings
- "Most of the ball was over the line." That is not enough; the whole ball must be over.
- "The line belongs to the field." Correct: the lines are part of the area they mark, so a ball touching the line is still in play.
See also the pitch markings guide to understand where the goal line sits.