VAR joins a far more high-tech refereeing tool introduced during the 2014 World Cup in Brazil, called Goal-line Technology (GLT). Using technology like Hawk-Eye, a pioneer in the field, sensors track ball and player movements down to the millimeter to determine whether a ball has crossed the entirety of the goal-line. Chances are, if you’ve watched a tennis match in the last decade, you’ve seen this technology used to determine whether a ball is in or out of bounds.

GLT saw some action at the 2014 World Cup. France’s Karim Benzema became the first player to have a goal confirmed by the system in a match against Honduras. The technology at this year’s competition will again be provided by GoalControl. The Germany company uses 14 high-speed cameras—seven focused on each goal—to track the movement of the ball, render it in 3D, and determine whether it crossed the goal line. Within one second, GoalControl’s system will process its decision and send it to the on-field referee, who wears a special smartwatch that alerts him whether to award a goal or not.

Some fear VAR could mar this year’s cup: Although deferring to a group of referees to check contentious plays should make the on-field referee’s life easier, it’s still his decision on when to engage VAR or not. The rollout in national leagues has not gone smoothly—there have been glitches, and confusion around when to use it, and the time it takes to get a thorough response from the VAR team can slow down a game. At an exhibition match between Spain and France last year, it took 40 seconds to make a VAR decision, which could really drag a game down if it has to be stopped multiple times in a row. For sports like American football, basketball, or tennis, where there are constant natural stops in play, video reviews are less intrusive into the game. But for the beautiful game—where halves should flow for 45 minutes, barring stops for free kicks or injuries—it could impact the rhythm of the game.

It’s entirely possible, with these two sets of technologies, that a faceless entity—a computer or a group of referees in a room, miles away from the game—could determine the outcome of a game in this year’s World Cup, including the final. How will 3 billion viewers react to that?

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