How it got into the Laws
The Royal Dutch Football Association ran the early experiments, and the IFAB sanctioned live trials from 2016. Australia's A-League became the first top-flight league to use a video assistant in 2017; the Bundesliga and Serie A followed for 2017–18. In March 2018 the IFAB voted the protocol into the Laws of the Game, and it was used at the World Cup in Russia that summer. La Liga adopted it for 2018–19 and the Premier League for 2019–20, later than most of its peers.
The four categories
The VAR may only intervene in four kinds of decision: goals and offences in the attacking move leading to them; penalty decisions; direct red cards, but not second yellow cards; and mistaken identity, where the referee cautions or sends off the wrong player. Everything else, from a throw-in given the wrong way to a free kick in midfield, stays with the on-field officials however wrong it looks on replay. The list is deliberately short, and the IFAB summarised the intent as "minimum interference, maximum benefit".
Check, then review
The VAR sits in a video operation room with an assistant VAR and a replay operator, and checks every incident in the four categories as play continues. Most checks end silently. If the VAR believes there has been a clear and obvious error, or a serious incident the officials missed entirely, a review is recommended. Two routes follow. For factual matters, whether a player was in an offside position, whether the ball left the field, whether an offence occurred inside or outside the penalty area, the VAR decides and tells the referee; this is a VAR-only review. For subjective matters, such as whether a challenge was a foul or a handball was deliberate, the referee goes to the referee review area, watches the footage and decides. The Laws are explicit that the referee keeps the final decision in every case.
One practical consequence is the delayed flag. Assistant referees are instructed to keep the flag down in tight offside situations where a goal may follow, so that the attack can be reviewed afterwards rather than killed by a wrong flag. That is sensible on its own terms and irritating to watch, and both things are true at once.
Working note
"Clear and obvious" is not a quantity. Two competent officials looking at the same challenge can disagree about whether the referee's call was defensible, and the protocol gives no test for settling that disagreement. This is the source of most VAR arguments, and better cameras do not touch it.
Offside: from hand-drawn lines to tracking
Until recently offside was judged by an operator scrubbing broadcast footage, usually at 50 frames a second, to find the frame where the ball was kicked, then drawing calibrated lines from the relevant body parts. Two sources of error follow. Picking a frame one either side of the true kick moment moves the players by whatever they travel in 20 milliseconds, and deciding which part of a shoulder counts is itself a judgement. Competitions have handled this differently; the Premier League, for example, has at times adjusted its tolerance for how thick the drawn lines are, and has said so publicly.
Semi-automated offside changes the inputs. At the 2022 World Cup in Qatar FIFA installed twelve dedicated tracking cameras under each stadium roof, tracking 29 points on every player at 50 frames a second, and used a ball with a sensor reporting 500 times a second to fix the kick moment. The system alerts the VAR to an offside position; a human still confirms it, and still decides whether the player was interfering with play. Serie A adopted a version in 2023 and the Premier League introduced it during the 2024–25 season. What it removes is the frame-picking and the line-drawing. What it leaves is the rule itself: a toe beyond the line is still offside, with no margin, which is why some have argued for the IFAB to trial a "daylight" standard in youth competitions.
Trade-offs and comparisons
The clearest cost of VAR is time, and the clearest complaint is silence. Rugby union broadcasts the referee's conversation with the TMO and shows the replays on stadium screens; football historically did neither, and the Premier League's later release of edited officials' audio in a separate programme shows how far behind it started. FIFA trialled referees announcing decisions to the crowd at the 2023 Club World Cup and Women's World Cup. Whether more openness reduces the arguments or merely makes them better informed is genuinely uncertain.
Set against cricket, football's protocol is the odd one out. DRS gives the on-field umpire a structured margin through umpire's call; rugby's TMO protocol has the referee announce an on-field decision first and requires clear evidence to move it; VAR has the high-threshold idea but no mechanism to express it, so the threshold moves with the personnel in the room. Semi-automated offside tidies the one factual question that was being handled worst. The subjective ones remain what they always were, and the honest expectation is that they will keep being argued about.