While fans of tennis and rugby will be familiar with technology affecting the game – those sports deploying Hawkeye and the Television Match Official (TMO) respectively – this is the first time in history that football has featured VAR at a World Cup.
And it’s already proving controversial. Here’s everything you need to know. It’s a little complicated but there’s method in the madness.
What is it?
Regardless of where the match is being played, the VAR team is located in a centralized operation room in Moscow.
That team – made up of one lead video official and three assistants – has access to all 33 of the broadcast cameras inside the stadium, of which 12 are slow-motion.
They also have two additional cameras dedicated to monitoring possible offsides, featuring computer-generated lines projected onto the field of play. For the knockout phase, an additional ultra slow-motion camera will be installed behind each goal.
The VAR team don’t only review footage on the instruction of the referee. They’re constantly checking for “clear and obvious” errors behind the scenes.
It’s important to note VAR is only used in what FIFA deems to be “game-changing” incidents. These are goals, penalty decisions, direct red cards and cases of mistaken identity.
How does it work?
Communication between the referee and the officials watching the video footage is two-way. If the VAR believes the referee has made a mistake, they can advise him at any time via the headset.
If the on-field referee is unsure of a particular decision, he can make contact with the VAR.
Many of the venues for Russia 2018 are thousands of miles away from capital, so communication is made through what FIFA calls a “sophisticated fibre-linked radio system.”
Photos: Eleven cities, 12 stadiums
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St. Petersburg Stadium, Saint Petersburg —
Designed by late Japanese architect Kisho Kurosawa to look like a spaceship, the brand new St. Petersburg Stadium was built on Krestovsky Island where the 110,000-capacity Kirov Stadium used to stand.
Photos: Eleven cities, 12 stadiums
OLGA MALTSEVA/AFP/AFP/Getty Images
St. Petersburg Stadium, Saint Petersburg —
Opened in April 2017, the stadium is equipped with a retractable roof and sliding pitch. Inside, the temperature can be regulated to a mild 59 degrees Fahrenheit (15 C) all year round.
Photos: Eleven cities, 12 stadiums
MLADEN ANTONOV/AFP/AFP/Getty Images
St. Petersburg Stadium World Cup schedule: Group stage, last 16, semifinal, third-place playoff Legacy: The 67,000-seater will regain its former name -- Krestovsky Stadium -- and be home to 2007-08 UEFA Cup winners Zenit St. Petersburg.
Photos: Eleven cities, 12 stadiums
KIRILL KUDRYAVTSEV/AFP/AFP/Getty Images
Ekaterinburg Stadium, Yekaterinburg —
Located 1,000 miles east of Moscow on the site of the old Central Stadium -- once a prominent speed skating venue -- the Ekaterinburg Stadium has retained its original Soviet neo-Classical pillars while adding modern refurbishments and temporary stands.
Photos: Eleven cities, 12 stadiums
FIFA
Ekaterinburg Stadium, Yekaterinburg —
The additional seats, constructed outside of the original stadium, loom dramatically at either end of the pitch in order to fulfill FIFA's minimum World Cup capacity of 35,000. Recent inspection reports have shown the temporary stands "fully comply with all safety and security requirements," according to a FIFA spokesperson.
Photos: Eleven cities, 12 stadiums
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Ekaterinburg Stadium World Cup schedule: Group stage Legacy: FC Ural, one of Russia's oldest clubs newly promoted to the country's top tier, will continue to use the stadium for its home games. After the World Cup, the capacity will be reduced and it will once again be known as Central Stadium.
Photos: Eleven cities, 12 stadiums
FIFA
Fisht Stadium, Sochi —
The Fisht Stadium held the opening and closing ceremonies of the 2014 Winter Olympics and is already well-equipped for the demands of a major international football tournament.
Photos: Eleven cities, 12 stadiums
FIFA
Fisht Stadium, Sochi —
Named after Mount Fisht, a peak in the nearby Caucasus mountain range, the arena's roof was designed to resemble a snow-capped summit.
Photos: Eleven cities, 12 stadiums
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Fisht Stadium World Cup schedule: Group stage, last 16, quarterfinals Legacy: The 47,700-capacity venue will stage training camps and competitive matches for the Russian national team.
Photos: Eleven cities, 12 stadiums
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Luzhniki Stadium, Moscow —
It was home to the 1980 Summer Olympics, 2008 Champions League final, 2013 Athletics World Championships and no shortage of musical tours, from Michael Jackson to the Rolling Stones...
Photos: Eleven cities, 12 stadiums
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Luzhniki Stadium, Moscow —
Now the Luzhniki Stadium has been refurbished -- with the athletics track removed and two extra tiers added -- while preserving its historical facade.
Photos: Eleven cities, 12 stadiums
DMITRY SEREBRYAKOV/AFP/AFP/Getty Images
Luzhniki Stadium World Cup schedule: Group stage, last 16, semifinal, final Legacy: The 81,006-seater will retain its status as the country's leading football stadium, hosting competitive international matches and friendlies.
Photos: Eleven cities, 12 stadiums
Handout/Getty Images Europe
Kaliningrad Stadium, Kaliningrad —
Built in the heart of Kaliningrad on Oktyabrsky Island -- a section of land sandwiched between Poland and Lithuania left largely untouched until its selection as a World Cup venue -- the Kaliningrad stadium is loosely based on the design of Bayern Munich's Allianz Arena.
Photos: Eleven cities, 12 stadiums
FIFA
Kaliningrad Stadium, Kaliningrad —
Kaliningrad Stadium World Cup schedule: Group stage Legacy: The 35,000-seater stadium will have its capacity reduced by 10,000 and be home to second-tier side FC Baltika Kaliningrad. A new residential development will be built around it featuring parks, quays and embankments alongside the Pregola river.
Photos: Eleven cities, 12 stadiums
FIFA
Rostov Arena, Rostov-on-Don —
Located about 20 miles from the Sea of Azov in south eastern Russia, the brand new Rostov Arena is 51m tall -- as high as the Niagra Falls.
Photos: Eleven cities, 12 stadiums
MLADEN ANTONOV/AFP/AFP/Getty Images
Rostov Arena World Cup schedule: Group stage, last 16 Legacy: As one of the first major projects built on the southern bank of the Don River, architects hope the 45,000-seater stadium will attract a flow of people and investment from the north. It will also host Russian Premier League side FC Rostov's home fixtures.
Photos: Eleven cities, 12 stadiums
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Volgograd Arena, Volgograd —
Built at the foot of the towering Mamayev Kurgan World War II memorial "The Motherland Calls" (pictured), the Volgograd Stadium will replace the demolished Central Stadium and feature an open lattice exterior structure.
Photos: Eleven cities, 12 stadiums
MLADEN ANTONOV/AFP/AFP/Getty Images
Volgograd Arena World Cup schedule: Group stage Legacy: The 45,000-seater will become the home ground of second-tier side FC Rotor Vologograd.
Photos: Eleven cities, 12 stadiums
FRANCOIS XAVIER MARIT/AFP/AFP/Getty Images
Spartak Stadium, Moscow —
Built to host Spartak Moscow -- the "people's team" which has made do without its own venue for almost a century -- the 43,298-seater Spartak Stadium will go on proving its worth long after the World Cup. The arena's facade features hundreds of red and white diamonds representing Spartak's logo, which change color when the Russian national side plays there.
Photos: Eleven cities, 12 stadiums
FRANCOIS XAVIER MARIT/AFP/AFP/Getty Images
Spartak Stadium World Cup schedule: Last 16 Legacy: As well as hosting Spartak Moscow and the national side, the stadium will provide the center piece for a new residential development.
Photos: Eleven cities, 12 stadiums
MLADEN ANTONOV/AFP/AFP/Getty Images
Nizhny Novgorod Stadium, Nizhny Novgorod —
Situated at the confluence of the Volga and Oka rivers, the new Nizhny Novgorod Stadium is designed to resemble the shimmering waters that surround it. The 45,331-capacity arena sits close to the Alexander Nevsky cathedral, and with views across to the Nizhny Novgorod Kremlin.
Photos: Eleven cities, 12 stadiums
Andrey Orekhov
Nizhny Novgorod Stadium World Cup schedule: Group stage, last 16, quarterfinals Legacy: The stadium was intended to become the permanent home of Russian club FC Volga, replacing the Lokomotiv Stadium after the tournament. However, Volga dissolved because of financial troubles in June 2016. Instead, second tier Olympiets Nizhny Novgorod will call the new build home.
Photos: Eleven cities, 12 stadiums
MLADEN ANTONOV/AFP/AFP/Getty Images
Samara Arena, Samara —
Constructed in a southeastern region renowned for its aerospace sector, the 44,807-seater Samara Arena is designed to resemble an otherworldly glass dome. By night, the whole structure will light up.
Photos: Eleven cities, 12 stadiums
MLADEN ANTONOV/AFP/AFP/Getty Images
Samara Arena World Cup schedule: Group stage, last 16, quarterfinals Legacy: The 44,918-capacity stadium will be known as Cosmos Arena, hosting Russian second-tier side FC Krylia Sovetov Samara.
Photos: Eleven cities, 12 stadiums
MLADEN ANTONOV/AFP/AFP/Getty Images
Featuring a striking orange, red and white exterior, construction on the 44,442-seater Mordovia Arena began in 2010. Initially hoped to be completed two years later for the 1,000th anniversary of the Mordovian people's unification with Russia's other ethnic groups, it was eventually finished in April 2018.
Photos: Eleven cities, 12 stadiums
MLADEN ANTONOV/AFP/AFP/Getty Images
Mordovia Arena World Cup schedule: Group stage Legacy: With a population of just 300,000, Saransk is the smallest of the 2018 World Cup host cities. After the tournament, some of the stadium's temporary structures will be demolished, reducing the capacity to 25,000. It will become the home of third-tier side FC Mordovia.
Photos: Eleven cities, 12 stadiums
ROMAN KRUCHININ/AFP/AFP/Getty Images
Kazan Arena, Kazan —
Designed by the same firm of architects as Wembley and Arsenal's Emirates Stadium, Kazan Arena was constructed to blend seamlessly into the surrounding landscape. Viewed from above, it is said to resemble a water-lily on the banks of the adjacent Kazanka river. The front of the stadium is dominated by a high definition screen with a total area of 3,700 meters -- the largest of its kind in the world.
Kazan Arena World Cup schedule: Group stage, last 16, quarterfinals Legacy: Opened in 2013, it will continue to be home to Rubin Kazan, Russian Premier League champions in 2008 and 2009. Visit CNN.com/sport for more news and features
Crucially, the VAR does not make any decisions. Instead, they work in an advisory capacity for the man with the whistle. The final decision can only be taken by the on-field referee.
Whether the referee accepts information from VAR or reviews the footage himself on a screen at the side of the field, depends on the type of incident.
Some game-changing incidents like fouls, or possible offside calls leading up to a goal, are strictly in the remit of the on-field referee.
“Factual” game-changing incidents, however, like whether the ball went out of play leading to a goal will be relayed to the referee via the headset.
If the on-pitch referee wants to assess the footage himself, he will do so in the aptly-named “referee review area” – located near the benches – on a pitch-side mobile screen.
How do I know VAR is being used?
The referee can delay the restart of play at any time to communicate with the VAR team in Moscow. This is signaled by the referee pointing to his headset.
If an official VAR review is initiated, the referee will gesture with his hands drawing the outline of a screen to let the players know the game has been stopped.
VAR has already shaped the course of numerous games in the first week of the tournament, helping the referee award decisive penalties to France and Sweden.
