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 their 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, since 2014, the Men's and Women's FIFA World Cups.
Background
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.
Rules
Since 2012, goal-line technology has been permitted in matches. Text relating to goal-line technology can now be found within four of the Laws of the Game:
Law 1 (The Field of Play): permitting modifications to the goal frame. Law 2 (The Ball): permitting the use of approved balls with integrated technology. Law 5 (The Referee): requiring the referee to test a goal-line technology system prior to a match and not use it if a fault is found. Law 10 (Determining the outcome of a match): permitting use of goal-line technology to verify whether or not goals have been scored. It states that "the use of GLT must be stipulated in the respective competition rules".
The Laws themselves are not specific as to the nature of goal line technology systems, however other documentation from FIFA, which is cited by the Laws, goes into more detail. The FIFA Quality Programme for GLT Testing Manual precisely define the requirements of the systems. Four basic requirements of a system are stipulated:
The system must address only the matter of whether a goal has been scored or not. The system must be accurate. The system must indicate the scoring of a goal immediately, confirming this within one second. The system must communicate its information solely to the match officials (via vibration and visual alert on the referee's watch)
FIFA have a system whereby a particular technology provider needs to show effectiveness to successfully obtain a license for their technology, then an installation within a particular stadium must pass a "final installation test" before use, and before each game the referee must check that the system is functional.
Competitions using goal-line technology
Due to the expense of goal-line technology systems, the technology is only currently used at the very top levels of the game. In domestic competition, goal-line technology is only regularly used in a few major European leagues: