Currently making waves throughout European football, VAR — or Video Assistant Referee to give the concept its full name — was introduced in the Bundesliga for the 2017/18 season, and has been helping officials make correct decisions ever since.

bundesliga.com lays out what VAR is and how it is being used to make football a fairer sport.

How does it work?

Each Bundesliga game, and from 2019/20 each Bundesliga 2 match, has a VAR, who sits in the VAR studio in Cologne and can quickly review incidents that occur in order to help the referee on the pitch. After watching TV replays, the VAR gives their opinion to their counterpart inside the stadium via the earpiece worn by match officials. The referee on the pitch will then signal as usual for the decision or make a rectangle shape with their hands to either signal an on-field review or that the original decision has been changed. The decision is then also shown on screens around the ground to communicate the final decision to spectators.

Watch: How Video Assist works

Which incidents are looked at?

There are four clear cases in which a VAR can review incidents via TV replays.

1) Goals
Were there any infringements leading up to a goal, including offside, fouls or the ball going out of play? Was a goal ruled out for an infringement correctly disallowed?

2) Red cards
Is the sending-off justified? Have the on-field officials missed any serious foul play or misjudged a foul?

3) Penalty
Is the decision to award the spot-kick correct? Should one have been given for a foul not spotted by the match referee?

4) Yellow/red cards
Is there a case of mistaken identity? It must be noted that VAR cannot intervene to judge the merits of yellow cards, only reds.

Referees are able to take advice from the VAR in Cologne or consult the pitch-side TV monitor to review their decisions. - imago images/Sven Simon

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Who has the final say?

The VAR can only give their opinion. The match referee has three options when they hear what their colleague has to say:

leave their decision unchanged;
accept the VAR's suggestion regarding a decision;
watch the incident again themselves via a TV screen inside the stadium.

When was VAR used for the first time?

Tobias Stieler was helped by Dr. Jochen Drees, the very first VAR for a Bundesliga game, when Bayern Munich kicked off the 2017/18 league season with a 3-1 win at home to Bayer Leverkusen. The VAR was called on 12 times in the match, helping to spot a foul by Leverkusen's Charles Aranguiz on Robert Lewandowski that led to a penalty being awarded to Bayern that otherwise would not have been given.

Where is it used?

Following trials by the Dutch Football Association in the early 2010s, the Laws of the Game were amended by the International Football Association Board to allow VAR to be used in matches and lead to its full introduction.

The A-League in Australia was the first professional top-flight competition in the world to employ the system, later used in the MLS and at international level for the first time in the 2017 FIFA Confederations Cup.

It was introduced to the Bundesliga in 2017/18, as well as Italy’s Serie A, before undergoing further trails in Spain’s La Liga, the FA Cup in England and France’s League Cup. During that season, VAR was officially written into the Laws of the Game by the IFAB and its use was confirmed at the summer’s FIFA World Cup in Russia. Since then the system has been adopted in a number of major club competitions, including England’s Premier League and the UEFA Champions League, as well as Bundesliga 2, from 2019/20.