World Football - Factbox: Goal line technology
Factbox on goal line technology which has been approved by the International Football Association.
The technology will be used exclusively in situations where it is not clear if the ball has actually crossed the goal line, such as when it bounces down off the underside of the crossbar and is then cleared away by a defender.
UEFA president Michel Platini is among those worried that the introduction of goal line technology will lead to calls for the use of further technology in offside, handball and penalty decisions.
The use of goal line technology will be optional.
Two systems have been approved for use. One is manufactured by British company Hawk-Eye, which is used in tennis and cricket and is based on optical recognition with cameras. The other is GoalRef, a German-Danish creation, using a magnetic field with a ball equipped with a microchip to identify a goal situation.
In both systems, a signal is sent to the referee within one second indicating whether the ball has crossed the line.
This differs from tennis and cricket, where graphics appear on giant screens indicating the trajectory of the ball before the decision is made.
In tennis, Hawk-Eye is used for disputed line calls with each player allowed to challenge up to three calls per set. In cricket it is used to determine calls in disputed lbw decisions, whether the batsman got an edge to the ball in being caught behind and in run out calls.
The debate over the use for goal line technology has been raging for at least a decade.
It gained momentum in 2005, during a Premier League game between Manchester United and Tottenham Hotspur. United goalkeeper Roy Carroll failed to hold a long-range shot by Pedro Mendes and the ball slipped over the line before it was cleared.
However, the referee and his officials waved play on.
FIFA tested a system using a microchip inside a ball at the U17 World Championship in Peru in 2005 but was not satisfied with the result In March 2010, the International Football Association Board shelved all discussions over the introduction of goal line technology.
Although the ball clearly crossed the line after hitting the underside of the crossbar, the Uruguayan trio of match officials did not see it. Germany, winning 2-1 at the time, went on to win 4-1.
Last season's Serie A title was influenced by a ghost goal in the AC Milan-Juventus top-of-the-table match. Milan were denied a 2-0 lead when Sulley Muntari's header crossed the line, but was clawed away by Gianluigi Buffon as officials waved play on. Juventus hit back to draw 1-1 and went on to win the title.
OTHER GHOST GOALS
The most famous goal line incident was at the 1966 World Cup final. England and West Germany were drawing 2-2 in extra time when Geoff Hurst's shot hit the underside of the crossbar and bounced down onto the line. After consulting his linesman, the referee gave the goal and England went on to win 4-2 amid German protests.
At the 1986 World Cup, Spain's Michel saw a shot hit the underside of the crossbar against Brazil, bounce over the line and out again. The goal was not given and Brazil went on to win 1-0 Ten years later at Euro 96, officials failed to spot that Dorinel Munteanu's effort for Romania against Bulgaria had crossed the line in similar circumstances. Romania lost 1-0 and were eliminated.
Replays showed it had crossed the line, but the Tunisian referee did not award the goal. The result led to rioting outside the stadium.