Diagram of a Goal Line Technology system based around sensors in the ball and goal frame. Most operational systems instead use cameras to track the ball
In association football, goal-line technology (sometimes referred to as a Goal Decision System) is the use of electronic aid to determine if a goal has been scored or not. In detail, it is a method used to determine when the ball has completely crossed the goal line in between the goal-posts and underneath the crossbar with the assistance of electronic devices and at the same time assisting the referee in awarding a goal or not. The objective of goal-line technology (GLT) is not to replace the role of the officials, but rather to support them in their decision-making. The GLT must provide a clear indication as to whether the ball has fully crossed the line, and this information will serve to assist the referee in making his final decision.
Compared to similar technology in other sports, goal-line technology is a relatively recent addition to association football; its integration having been opposed by the sport's authorities. In July 2012, the International Football Association Board (IFAB) officially approved the use of goal line technology, amending the Laws of the Game to permit (but not require) its use. Due to its expense, goal-line technology is only used at the highest levels of the game. Goal-line technology is currently used in the top European domestic leagues, and at major international competitions such as the 2014 Men's, 2018 Men's and 2015 Women's FIFA World Cups.
In association football, a goal is scored if the whole of the ball crosses the goal line between the goalposts and under the crossbar. In most cases, this is relatively unambiguous (goal nets being a low-tech way of verifying that the ball passed the correct side of the goalposts). Occasionally however situations occur when it is difficult for referees and their assistants to tell if a goal has been scored before a rebound, save, or defender's clearance from the goal area.