In the 39th minute of a 2010 second-round World Cup soccer game, England's Frank Lampard shot the ball at Germany's goal. The ball hit the crossbar of the goal net, bounced down to the ground and back up to the bar again before the German goalie grabbed it out of harm's way. The officials called it a no-goal, because the ball had not fully crossed the white goal line on the pitch that runs parallel to the cross bar. But it had. Video replay showed clearly that Lampard's shot had hit the ground nearly a third of a meter inside the goal line before bouncing back up. But the call was final, and the Germans had the ball. England lost that game and was eliminated from the World Cup.

Lampard's goal-that-wasn't immediately reignited a debate that has been simmering in soccer for years. Should the sport install goal line technology—sensors that would tell referees exactly when the ball has passed that crucial white line? Many see the England–Germany game as a prime case for why soccer needs to embrace technology. But for a long time, the International Football Association Board (IFAB), which oversees the international rules of soccer, was cold to the idea of adding any kind of technology to the game. Instead, they introduced two new referees to watch the goal line.

With so many players hovering close by, however, those extra refs cannot always see clearly. Case in point was another missed call at this year’s Euro Cup, which used the five-referee system. In the 62^nd minute of a crucial game, the Ukrainian striker Marco Devic launched a ball that bounced off England’s goalkeeper and toward the goal line, before an English defender cleared it. The goal referee called it a no-goal, but replays showed the ball crossed the line. The goal would have put Ukraine even with England 1-1, but without it they lost 1-0, and were eliminated from the tournament. Afterward, Sepp Blatter, president of the sport’s governing body, FIFA (Fédération Internationale de Football Association), tweeted: "After last night's match GLT [goal line technology] is no longer an alternative but a necessity."

Before the Euro Cup, the IFAB had changed its mind and gave the green light to try goal line sensors from two of 10 competing companies: GoalRef and Hawkeye. In early July, IFAB approved both technologies, although they will remain optional. FIFA said it will use goal line technology for future matches, including the next World Cup, in 2014 in Brazil.

The two companies have quite different approaches. Hawkeye's system—many details of which are under wraps until after this round of testing ends—is based on the same technology you might have seen at top-tier tennis matches. A series of cameras positioned around the soccer field will watch the ball and calculate its position in the air to determine whether it fully crossed the plane of the goal. If a referee's call on the field is controversial, officials can look at the Hawkeye replay—the same way tennis officials, and fans, can now see precisely whether the ball landed inside, on or outside a line.

GoalRef uses a completely different system. There are no cameras and no high-powered computers crunching video. Instead, GoalRef relies on a low-level magnetic field spanning the goal opening. Wires inside the goal posts generate the field, and wires inside the ball disrupt that field after the ball completely passes through the opening. The system then alerts the referees that the line has been crossed.

6 Comments

1. 1. promytius 11:22 AM 7/26/12

   'Professional' sports are not science. They are simply money-making machines for the ultra-rich. I really don't care what they use to decide anything in sports, because it is all completely irrelevant to reality. It's a stupid game (and you may substitute ANY 'professional' sport) played by millionaires for other millionaires' profits, so I suggest that instead of figuring out how to score the stupid ball, why not just auction the goals off? Money talks. Or, they could just admit it's all about money and get on with it, but there is no USEFUL science in monitoring a goal, a plate, a line on the ground, or in the air. Self-indulgence at its most avaricious, too silly for SA to even comment on, never mind feature an article.

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2. 2. Bora Zivkovic 01:24 PM 7/26/12

   Interesting approaches. As I started reading this article, I thought to myself I'd use LED diodes emitting infrared light beams, positioned all along the top bar, beaming down to an array of receivers connected to the computer. When the ball breaks any one of those beams, the receiver detects the loss of infrared light and notifies the computer which emits a loud sound.
   
   This is what I used to do in my own research (and built the whole system from scratch, using the oh-so-wonderful Dremmel tool). But then I thought at the false positives I sometimes got and realized those would be even worse in soccer - the system is dumb, and would not be able to differentiate between the ball crossing the line and the goalie (or any other player, or a bird, or clump of dirt) crossing the line.
   
   So I really like the magnetic ball crossing the magnetic field system. It is simple, robust, and gives a clear yes-or-no answer. The multi-camera system appears to be too complex, thus more prone to subtle errors.
   
   Also, while it must have felt good for @promytius to vent here, I did not see this article to be about sociology, economics or politics of sport. His comments, being OT, could potentially be removed according to our commenting rules.

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3. 3. jandone 01:46 PM 7/26/12

   Scoring used to be so easy. If your ball bounces back, it meand you did not deserve that goal. There is a reason they put the net there to catch scored goals.

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4. 4. verhappy 03:16 PM 7/26/12

   Picking up from Bora, I wonder why a simple 5 camera system installed into the goal posts wouldn't work? With the size of security cameras and the like, I don't see a reason that the cameras couldn't be installed as follows:
   
   One recessed into the bottom middle of the cross bar with a fish eye lense--if the ball crosses the line you would see dark between the line and the ball. This one would be covered with a resilient plastic protector to blend it into the goal post;
   Two in each upper corner of the net where they would need minimal recessing since the ball could not touch the deepest corner;
   Two just recessed just a metre or so above the ground in the same way the cross bar was. With these five camera angles on each net it should be obvious whether the ball crosses the plane of the net.
   
   For insurance, a slightly reflective strip or bright colour could be placed on the inside edge of the goal posts so that if the ball is in the air the cameras could pick up from comparison whether it has crossed the line. The magnetic field sounds interesting, but I wonder about false negative should there ever be a malfunction in the wire within the ball? How would they be able to ensure the ball's wire is operational at all times during the game?

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5. 5. hb 03:43 PM 7/26/12

   In both matches mentioned, TV viewers (including soccer officials not involved in the game) could clearly see that the ball had crossed the goal line. In a controversial situation all it would take is for the attacking team to be able to request a review, much as tennis players can demand slo-mo replays of questionable calls. Play would only need to be halted long enough for communication between the referee and an extra official in the TV booth; that official would then make the final decision based on evidence available to every TV viewer. Misuse of the right to request a review should simply draw yellow cards.

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6. 6. jackvandijk 04:41 PM 8/9/12

   voetbal is futbal, no electronics. if the referee makes an error, that is part of the game.

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