The international football friendly (the association kind) between England and Belgium scheduled for June 2 may not be burning a hole in your diary, but it will be notable in at least one respect. The match, to be held at London's Wembley Stadium, will be the highest profile match to date to make use of so-called goal-line technology, designed to detect whether or not the ball has crossed the line (and therefore whether a goal should be given). The goals at Wembley have been fitted with a Hawk-Eye system similar to those now officially used to assist umpires in tennis and cricket. However, though the system will be up and running for the entire match, it will not be used to help adjudicate in the event of a difficult goal-line decision.
Advocates of goal-line technology hope that it will eradicate erroneous decisions that can occur when it isn't clear whether or not the ball has crossed the goal-line. The tenth law of association football states that the whole ball must cross the goal-line for a goal to count. Currently such decisions are in the hands of the on-field referees and assistants, who sometimes have to make decisions based on blink-and-you'll-miss-it visual evidence, as a defender attempts to clear a ball, or a spinning ball bounces back out of the goal having ricocheted off the crossbar.
If football's governing body, FIFA, really wanted to put the technology through its paces, England should perhaps have hosted Germany. In possibly the most famous example of a controversial goal-line decision, during extra time in the 1966 World Cup final in London's old Wembley Stadium, Geoff Hurst's shot bounced out of the goal having hit the crossbar, but the goal was allowed giving England a 3-2 lead over West Germany. England went on to win the match 4-2, and Geoff Hurst remains the only man to score a hat-trick in a world cup final. However, a 1996 study at the Engineering Department at Oxford University concluded that the ball was 6 cm (2.4 inches) short of being a goal.
Balance was arguably restored during the 2010 World Cup in South Africa, when Frank Lampard's goal for England against Germany, which also bounced out of the goal having hit the crossbar, was disallowed, though video replays show the ball cleared the line by several inches. Had the goal been allowed England would have drawn level at 2-2. As it was, Germany went on to win 4-1 - a result which may go some way to explain the (English) Football Association's advocacy of goal-line tech.
The Hawk-Eye system uses a minimum of four cameras to track the trajectory of a moving ball. At Wembley, six cameras will be installed in each goal, each of which will monitor the location of the ball. By triangulating the ball's position from the images available, the system can notify the referee if the ball definitively crosses the line. Crucially, it can do this within a second (a FIFA stipulation) by transmitting a radio signal picked up by the referee's wristwatch.
Though used by cricket broadcasters since 2001, Hawk-Eye has only been used to help umpires adjudicate leg before wicket decisions since 2008, with the system extrapolating the trajectory of the ball to determine whether it would have gone on to hit the stumps had it not hit the leg of the batsman. Some dispute the accuracy of Hawk-Eye used this way, not least because cricket balls are wont to turn, bounce and swing an all manner of peculiar ways, though advocates argue Hawk-Eye is capable of taking all such behaviors into consideration.
Hawk-Eye technology has been used to assist with line decisions in tennis since 2006, perhaps with less controversy than in cricket. On the tennis court, Hawk-Eye is merely used to monitor where the ball has been, and so the predictive aspect of the technology does not come into play (as would be the case in football).
A competing technology, GoalRef, is also under consideration by FIFA. Unlike Hawk-Eye, GoalRef requires the ball to be chipped. Developed at the Fraunhofer Institute, GoalRef requires the football to be chipped and a magnetic field set up in the goal mouth. Sensors detect changes in the field when the ball crosses the line, notifying the referee nearly instantaneously. Though said to be cheaper than Hawk-Eye, FIFA may favor the camera-based system, if only for the dramatic replay-friendly footage the in-goal cameras will presumably record.
A vote on goal-line technology will take place at the next meeting of the International Football Association Board on July 2. Goal-line technology will need to meet with FIFA's approval if it is to pass the IFAB vote.