What made goal-line technology err in English Premier League game

Technology has reduced the margin of error in sports. A case in point is goal-line technology, which is now being used in all Premier League games to assist on-field referees. However, it seems the technology is not completely full proof. On the first day of the restart of Premier League, which was halted in March due to the covid-19 pandemic, an error by the goal-line technology denied Sheffield United a clear goal against Aston Villa. The game ended in a 0-0 draw.

Hawk-Eye Innovations, the company behind the technology later acknowledged the error. In an official post on Twitter, the company explained that the seven cameras located in 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 where this technology has been used.

The company added that the system was tested and proved functional prior to the start of the match in accordance with the laws of the game and were confirmed as working by match officials.

However, this is not the first time such goal technologies have erred during a game.

In the 2014 football World Cup, Germany-based GoalControl's goal-line technology first denied a goal to France against Honduras and soon reversed its decision to award the goal.

In 2018, France's League 1 also banned GoalControl's technology and switched to that of Hawk-Eye's after a bunch of controversial decisions.

Hawk-Eye's goal-line technology has a lot in common with that of GoalControl's but the former has been involved in fewer controversies. Hawk-Eye uses a pair of seven high speed cameras focusing on both goal posts to triangulate and track the ball’s precise position on the field. When the ball crosses the goal line it automatically alerts the referees.

Triangulation is a geometric technique used for determining the location of a point by forming triangles to it from known points. A software is then used to create a 3D image of the ball in relation to the line.

The objective of having multiple cameras watching from different angles makes goal-line technology effective. Even if some of the cameras are blocked by players, referees or goal posts during the game, at least one camera will get it right. Interestingly, in the Sheffield United vs Aston Villa game, all seven cameras are believed to have been blocked and that is what prevented the goal-line technology from detecting the goal.