Wellington Phoenix will break new ground in tomorrow night's friendly against Beijing BG at Westpac Stadium.
The Phoenix will become the first A-League team to play in a match with a live Video Assistant Referee (VAR) as part of ongoing trials into the new innovation.
Seven countries, including Australia, are involved in the trial, with Football Federation Australia hoping to "go live" in rounds 26 and 27 of this A-League season, as well as the finals series.
Trials have been going on in the background of A-League games since September, with VAR's making decisions without any contact with the referee and therefore no actual impact on the match. Tomorrow night's game will be the first time the VAR is in live contact with the referee.
Football Federation Australia's referee training and development manager Richard Beazley briefed the Phoenix players after their training session this morning and told them the VAR mantra is "Minimum influence, maximum benefit".
He explained that VAR's will be able to rule on four categories of "major game-changing incidents".
(1) 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?
(2) Penalties: Was a foul committed inside or outside the penalty area, has a penalty been missed or has one been wrongly awarded?
(3) Red cards: Was a potential send-off missed or was a red card wrongly issued?
(4) Mistake identity: Was a yellow or red card awarded to the wrong player?
The referee will be the sole judge of whether a video referral is initiated, but crucially, the VAR is able to suggest a referral, if they feel something has been missed by the man in the middle.
The referee is not obliged to act on any such suggestion, but it seems highly likely they would accept the advice, given the VAR has a "global" view of proceedings, while the referee has just one look, often for a split-second, in the heat of the contest.
Once the referee has decided to ask for a referral (either of his own accord, or on the suggestion of the VAR), he'll draw a box in the air in the same way cricket umpires do when requesting a review.
Play will halt, and the VAR will then examine all camera angles and deliver a decision back to the referee. The camera angles on offer will rely entirely on the game broadcaster, with anywhere from seven to 12 angles typically available.
If required, the referee himself can also look directly at TV replays on a screen set up for that purpose, which will be situated close to the fourth official's position between the two benches.
No time limit has been set for decisions to be made, but European trials suggest the average time to reach a verdict is 22 seconds, while some decisions can take over a minute. That time will be added at the end of the half.
The players themselves have no power over the referral system. In fact, players who attempt to influence the referee will be swiftly dealt with.
Any player making the TV signal to the referee will receive an instant yellow card, as will any player who enters the referee's TV review area. Any member of the coaching or support staff who enters the TV review area will be sent from the field.
Even the captain cannot approach the referee and request a referral.
It's not entirely clear yet what fans watching at home or on the big screen at grounds will see, although the suggestion is they'll see what the VAR is seeing, as they currently do in rugby and cricket.
One scenario that has occurred more than once in the A-League this season (and affected the Phoenix early in their campaign) is a player being wrongly flagged for offside, before going on to score a goal.
Under the new technology, the players were keen for assistant referees to err on the side of caution in tight situations, safe in the knowledge that if a player is in fact offside, it'll be picked up by the VAR.
However, Beazley was adamant they won't be asking their assistant referees to alter their behaviour, which caused some discussion among the players. As one pointed out, "Why wouldn't they just leave their flag down?"
It seems likely that this will eventually be the outcome, even if it's not specifically spelt out in the assistant referee's guidelines. If a player is offside and allowed to continue, the goal can always be chalked off on review.
But if a player is actually onside and wrongly flagged, the goal can't be retrospectively awarded, because there are too many other factors at play. More often than not, the game has stopped, because the referee has blown his whistle when he sees the flag go up.
Other scenarios were also posed. What if one side appeals for a penalty that isn't awarded and before a review can be initiated, the opposition wins the ball, goes down the other end and scores?
Beazley indicated that most VAR decisions will occur when the ball is out of play, suggesting that would be the case 90% of the time.
There was also some discussion around yellow cards not falling under the VAR brief, particularly those that lead to red cards. If a player is wrongly shown a second yellow card (leading to a sending-off), the decision cannot be reversed - only straight red cards can be examined by the VAR.
The basic tenet at the heart of the VAR trials around the world is pretty simple - will VAR's improve the game? On the face of things, more correct major game-changing decisions will be delivered, which has to be a good thing.
Goal-line technology in the English Premier League and other top competitions around the world has certainly been a success, with no doubt now over whether a ball has crossed the line or not.
The Phoenix and Beijing BG will play guinea pigs tomorrow night, taking football on the next step along the road of technological assistance and giving us our first chance to assess the value of the game's newest innovation.