The goal-line technology, another advance at the service of refereeing

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VAR, which we have thoroughly talked in previous articles of this blog, and the controversy that revolves around its use have seemed to hide any other technology connected to the world of football. The impact of VAR has been so huge that we tend to think that it has been the first step made to reach a fairer sport (although, as we have already confirmed in many occasions, VAR has not ended with hours and hours of debate between friends about if certain referee “has benefited” or “has harmed” a team), but the truth is that technologies destined to provide help to the referee’s collective came to football some years ago.

Today we are going to talk about a technology that lots of football lovers surely know: the goal-line technologies, also named as Goal Decision System. And we talk in plural because there is not only a single technology, but two different ways to introduce this technology, which we are going to explain in this post. We could even talk about a third method, which it is just the resultant of the mix of both systems.

Two goals that could change history

When the world of football started to experiment with technology applied to this sport, the first thing that experts tried to solve was not the offside problem, nor handball or penalties, but the ghost goals. The view of the main referee and its assistant referees is not always the best to judge if a ball has crossed or not the goal line in its entirety, especially when in the majority of situations is a matter of centimetres. Besides, the human eye has its limitations, and if you add the fact that everything on the field happens in a tenth of second, there is a breeding ground to provoke a referee’s mistake if the competition does not count with a technology that eliminates any doubt.

However, when was the detonator of this necessity of ending with the ghost goals? The own FIFA, in its website, mentions two key goals in the World Cup history that pushed the organization to investigate in this way and that confronted the same national teams: England and Germany.

1966. World Cup final. England, host of the event, and Die Mannschaft tied 2-2 at the end of the regulation time. In the extra time, Geoff Hurst, scorer of three goals in the aforementioned final, receives a ball with the back towards the goal, turns around and its shot smashes in the crossbar. The ball bounces near the goal line and the English players start to celebrate the goal. Geoff Dienst, referee of the match, agrees with England team after talking with its assistant, Tofiq Bakhramov: 3-2 for England, which would finished raising the title.

In 1995, research conducted by University of Oxford came to the conclusion that the ball has not fully crossed the goal line and therefore the goal did not have to count on the scoreboard.

Now, we move on until 2010 and the round of 16 of the World Cup celebrated in South Africa. With 2-1 in the scoreboard for Germany, Frank Lampard shoots from the edge of the box. Again, the crossbar gained a leading role by deflecting the ball downwards, although with a completely different ending compared to 1966: in this case, the ball clearly went into the goal, but the score did not change.

As we previously mentioned in our article about technology applied to sport, we can consider that the precursor of this idea is the commonly known as “hawk eye”, a system that has been used in the main tournaments of tennis (and other sports like cricket) since 2006 to check, after a request made by a player, if a dubious ball has entered or not in the field of play. In football, its implementation has similar principles and an (apparently) easy functioning  basically based on observation.

Some cameras are placed in the goals, each one in a different place around them in order to have a view of every possible. Those cameras that aims to the goal are placed in the grandstand of the stadium with the intention of having a more complete view of the ball.

Cameras constantly follow the ball and send a signal to a system that is capable of tracking the trajectory of the ball in 3D. When the ball crosses or not the goal line, the system recreates its position by the triangulation of the cameras, detecting the exact position of the ball to determine if it completely enters or not in the goal.

If the ball goes completely through the goal line, the program immediately sends a signal to the referee’s watch, which starts to vibrate. The live tracking of the cameras makes possible that the signal is sent to the referee in less than a second, ending with the controversy of the ghost goals.

Azor, our instant feedback multicamera system, is also based in this technology. Especially thought for assistant referees, one of the exercises that are used to do in the Azor sessions (and which can be seen in the next video) consists in a person placed under the crossbar bouncing a ball near the goal line. The assistant referee, after an sprint, must decide if the bounce was inside or outside the goal and goes to an screen in which they can instantly see if they have made the right or wrong decision thanks to the shot that has been recorded by a high-definition camera placed just in line with the goal line.

Technology based on magnetic fields

This detection system is a mix of two technologies in one: the magnetic field and the aerial or signal tools. This mechanism came later and is a bit more complex than the mentioned before, although its speed is tested and its accuracy approved by FIFA.

In this case there are not cameras because everything is based on a series of antennas placed along the posts and the crossbar and covered with plastic.

Besides, in the goal there is an underground inductor which is connected to a processor and, in turn, inside the ball we can found three electric coils. With this method, a magnetic field that covers the whole goal line is created.

When the ball surpasses the line, the antennas are activated and send a signal to the processor, notifying that it has crossed the magnetic field created in the goal. Just like in the case of the technology based on cameras, the referee’s watch receives a signal to confirm them that the goal is valid.

In Spain, none of these technologies had been implemented since the Supercopa 2020, in which the technology based on cameras was used for the first time. In LaLiga this function is also entrusted to VAR, although it means that the human factor comes into play to determine if the ball has crossed or not the goal line, so the error margin is a little bit bigger.

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