The Video Assistant Referee -- better known as VAR -- is under scrutiny again after one of its most chaotic incidents to date in Germany's top division on Monday.
The system is designed to help referees by giving them access to video reviews of key moments during games. However, it's only used to correct "clear and obvious mistakes" -- to allow or disallow goals, award or deny penalties, show or rescind red cards, or correct instances of mistaken identity when a referee disciplines the wrong player.
More VAR controversy
Players called back onto pitch from changing rooms
With the scores goalless in the Bundesliga match between Mainz and Freiburg, referee Guido Winkmann waved away appeals from the home side for handball in the penalty area, before promptly blowing the whistle for half time.
Having allowed both sets of players to enter the changing rooms, Winkmann then proceeded to call them back out onto the pitch after VAR had reviewed the penalty appeal and awarded the spot-kick.
Precisely six minutes and 44 seconds after the halftime whistle had initially blown, Mainz's Argentine forward Pablo de Blasis tucked the penalty away to give his side a 1-0 lead. The official time of his goal only read "45+1".
The decision, with Marc-Oliver Kempf clearly handling Daniel Brosinski's cross, was unquestionably the correct one, but the messy manner in which is was awarded will do nothing to win over critics of VAR.
Mainz fans then delayed the second half by 10 minutes after throwing rolls of toilet paper onto the pitch in protest against Monday night matches.
De Blasis would go on to double his team's lead with 10 minutes to go, handing his side a crucial three points to move above Freiburg in their battle against relegation.
As well as Germany, VAR technology has also been rolled out in Italy, Spain and the USA, among other countries, each to varying degrees of success, but later this year it will be used on the biggest stage of all: the World Cup.