Video Assistant Referees: All you need to know

This weekend the A-League will become the first top-tier football league in the world to introduce the Video Assistant Referee (VAR) system.

After almost a year of trials and training, the technology will "go live" for Round 26 and 27 of the 2016-17b A-League and the three weeks of finals.

Here's all you need to know about VARs. 

HOW WILL IT WORK?

Every A-League game will have a VAR assigned.

The VAR will view the game from a video operations room with access to up to 12 camera angles.

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If the VAR sees a clear error has been made, he will communicate that to the on-field referee.

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The on-field referee will then have the opportunity to ask for the decision to be reviewed by the VAR.

Upon review, the decision will potentially be overturned.

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WHAT CAN THE VAR RULE ON?

The VAR can rule on four different categories of "key match incidents": 

Goals

Did the ball cross the line, was there a foul or an offside missed in the build-up to the goal or did the ball go out of play in the build-up?

Penalty incidents

Was a foul committed inside or outside the penalty area, has a penalty been missed or has one been wrongly awarded?

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Direct red cards

Was a potential send-off missed or was a red card wrongly issued?

Mistaken identity

Was a yellow or red card awarded to the wrong player?

DOES THE ON-FIELD REFEREE HAVE TO TAKE THE ADVICE OF THE VAR?

No, but it's expected in the vast majority of cases, the on-field referee will take guidance from the VAR and change their decision if that is suggested.

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CAN THE ON-FIELD REFEREE ASK TO REVIEW THE FOOTAGE?

Yes. In rare circumstances, the on-field referee can run to the sideline and watch a replay.

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They can potentially change their decision based on that viewing.

WILL THE ON-FIELD REFEREES AND ASSISTANT REFEREES CHANGE THE WAY THEY OFFICIATE MATCHES?

No. Referees have been encouraged to control matches and make decisions in the same way they did before the introduction of VARs.

The VAR mantra is "minimum interference for maximum benefit".

The VAR will allow the referee to make their decisions, and only if a decision is clearly wrong will the VAR intervene.

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Where there is a clear error, the VAR is the "safety net" to catch that error.

CAN PLAYERS OR COACHES ASK FOR A DECISION TO BE REVIEWED?

No. Players and coaching staff are unable to influence the officials or request reviews.

HOW MANY VARs ARE THERE?

Nine VARs have been trained in the new technology in Australia and New Zealand.