How Does The Goal Line Technology Work?

By Matthew

30 December 2020 • 0:15GMT

 Since its introduction in the Premier League's 2013/14 season, Hawk-Eye's Goal Line Technology system has failed just once in over 9000 matches that it has been in operation. Of no doubt, the Goal Line Technology (GLT) has refined football, and so, how does it work?

GLT is basically a cluster of technologies that together monitors the path and movement of the ball and spots when it crosses the goal line. There are 4 major systems of the GLT approved by FIFA and the International Football Association Board (IFAB) which operate mainly by either camera tracking or magnetic field sensors.

•GoalControl

At the 2014 FIFA world cup, Brazil, GoalControl was the GLT system used. The German Company gained approval and certification just before the Hawk-Eye system. Before it was used at the world cup, it was successfully tested at the Confederations Cup and at the FIFA club world cup, 2013.

GoalControl uses camera tracking. 14 high speed cameras are mounted on the stadium roof (7 cameras per goal mouth) to capture the position of the ball in the air and on the ground. The referee receives a notification via his watch when the ball crosses the line.

•Hawk-Eye

Just like GoalControl, Hawk-Eye uses camera tracking. 7 cameras are installed at each goal, usually at the roof of the stadium. A software gathers the information from all cameras and then, tracks the ball in relation to the goal line. A signal is sent to the referee's watch within a second when the ball crosses the line. Ten seconds after, a graphical display of the ball's location is ready to be broadcasted.

Hawk-Eye is the present GLT system of the English Premier League and has been around since 2013.

Seven High Speed Cameras per goal mouth

•GoalRef

German Company, Fraunhofer IIS is the creator of GoalRef, a company that specialises in wireless communications. This GLT system uses magnetic field sensors built into the goal frames to detect the passing of the ball.

•Cairos GLT system

Cairos technologies and Adidas are the producers of this GLT system which also uses magnetic field sensors. In this system, a magnetic sensor is put into the ball. This sensor detects the magnetic field produced by thin wires underneath the penalty box. A computer then tracks the position of the ball using the sensor.

Another GLT system is GoalMinder which uses cameras built into goalposts and crossbars.

The Sheffield United Incident

A foul is being committed. It's a free kick to Sheffield on their left flank. Oliver Norwood is standing over the dead ball, ready to take the free kick and Aston Villa's defence is getting organised. Norwood sends a beautiful ball in, but Villa's goalie, Ørjan Nyland claims the ball in the air. As Nyland reaches for the ground, teammate, Keinan Davis bumps into him and then he is pushed together with the ball beyond the goal line. Nyland quickly presses the ball unto the goal frame, Sheffield United players are celebrating, the ball clearly crossed the line already.

Nyland is seen to have crossed the line with the ball. Photo Credit: Sheffield United TV

To their surprising disappointment, Referee, Michael Oliver doesn't award the goal, his wrist watch hasn't indicated, by vibration, that the ball crossed the line. Inevitably, this decision sparks a lot of controversies.

Hawk-Eye, the company that runs the league's goal line technology, after the match said that the view of the seven cameras were obstructed by the combination of the goalkeeper, defender and the post. Its statement read:

"During the first half of Aston Villa v Sheffield United match at Villa Park, there was a goal line incident where the ball was carried over the line by Aston Villa goalkeeper, No. 25 Nyland.

"The match officials did not receive a signal to the watch nor earpiece as per the Goal Decision System (GDS) protocol. The seven cameras located in the stands around the goal area were significantly occluded by the goalkeeper, defender, and goalpost. This level of occlusion has never been seen before in over 9,000 matches that the Hawk-Eye Goal Line Technology system has been in operation.

"The system was tested and proved functional prior to the start of the match in accordance with the IFAB Laws of The Game and confirmed as working by the match officials. The system has remained functional throughout. Hawk-Eye unreservedly apologises to the Premier League, Sheffield United, and everyone affected by this incident."

In 2013, when it was introduced to the Premier League, it was said that Hawk-Eye's high speed cameras had the ability to remove any player's picture obscuring the ball. It is still not understood why it didn't in this match.

After the match, Sheffield United's coach, Chris Wilder said he didn't know if he had to laugh or cry as he was deeply hurt by the decision. It cost them two points.

Sometimes, there are errors with all the technologies around but Goal Line Technology has been a huge success since its inception.