Florian Wirtz netted a goal at Fulham in January 2026 to make it 1-1, but he didn’t even celebrate. The assistant’s flag was held, and replays appeared to indicate his foot was outside the last defender and he was “fairly sure” it was out. Confusion like that can get fans talking, like the debate that breaks out in a taproom while beer lovers compare and contrast notes and come to grips with their initial impressions and the finer points of the latest release.
After a couple of moments, the review returned, and the goal was still there. That is why there are so many arguments surrounding offside in football. The fans see the line on the screen and think that a machine has measured a toe to the millimetre, but in reality it’s a series of cameras, sensors, software and people. If you follow that chain, you’ll see where its precision subtly ends.
Why The Human Eye Was Never Enough
Offside asks an assistant referee to watch two things at once that are often forty metres apart. They have to register the instant a pass is played and, in the same instant, the positions of an attacker and the second-last defender. The first version of VAR tried to fix this with replays. An operator scrolled through broadcast footage, picked the frame where the ball seemed to leave the passer’s boot, and then placed crosshairs on the relevant body parts so that lines could be drawn across the pitch.
Research has since shown how shaky that first step is. In a 2022 study at the University of Bath, Dr Pooya Soltani recorded passes with motion-capture equipment and asked viewers to pick the moment of the kick from ordinary footage. On average, their choice was about 132 milliseconds away from the measured liminal moment, which is a long time when players are running at full speed.
Why Football Handed The Call To A Machine
The reasoning behind the partly automated offside detection system is to remove those manual operations from humans. It was introduced at Qatar’s 2022 football tournament after a few tests, and UEFA has implemented it in the Champions League, while the Premier League adopted it after a season of testing and delays in April 2025. The word semi is important, as the software presents a solution, which must still be approved by a video official.
Handing a judgement to audited software is not unique to football, and the logic is the same wherever it happens. At an online casino such as crusino casino, nobody deals a card or spins a wheel by hand, so players rely on a certified random number generator, on game rules that are published in advance, and on a record of every round that can be checked afterwards. In both settings, people accept an outcome they cannot verify with their own eyes, because the process behind it is consistent and open to inspection.
The Three Measurements Behind Every Call
All offside judgements reduce to three questions that must be answered at the same time. The system must be able to determine the location of each player relative to a specific area of the body, the exact time the ball was played, and the position of the offside line at that time. There’s a piece of tech to each question, and each question adds a little bit of uncertainty. Each of them on its own makes sense as to why the final graphic looks so definitive.
Where Every Limb Is
Tracking cameras mounted under the stadium roof follow the ball and all twenty-two players throughout the match. At the 2022 World Cup there were twelve of them, recording up to 29 points on each player’s body fifty times per second. Newer systems go much further. The Premier League’s version, supplied by Genius Sports, uses as many as thirty cameras, several of which film at 100 FPS, and it builds a surface mesh of as many as 10,000 points for each player.
The Exact Moment The Ball Is Played
The kick point is the hardest part to pin down, because a ball stays on a boot for only around a hundredth of a second. FIFA’s answer was to put a sensor inside the ball itself, an inertial measurement unit that reports its movement 500 times per second. The sudden change in the ball’s motion can pinpoint the moment of contact more precisely than individual camera frames. The Premier League’s system doesn’t require any chip as it relies on camera data to identify the kick. The focus on detail is equally evident in the production of craft beer collabs, where precision of fermentation activity and temperature control help craft beer makers ensure consistency and quality in every batch.
Where The Line Falls
Once everything is set, it can identify the most recent defender and the body part that can legally score, which is the closest to the goal line. Hands and arms do not count for either player, so the model has to tell where the arm ends: the laws put the end of the arm at the bottom of the armpit. It then checks the highest scoring area of the attacker’s body against the line and tells the video room if the attacker has passed the line. Once the referee confirms the call, it is then converted into the 3D animation depicted in the stadium and on TV.
What The Officials Still Decide
This technology only reports if a player is on the other side; it’s not the same as an offence. There are some judgements to be made that are still in the hands of the people in the video room and the referee on the pitch.
- Confirming the proposal: the video assistant will verify the proposed kick point and line and will be able to adjust both manually if they are not correct.
- Only when it interferes with play or another player is being offensive is a player penalized for being offside.
- Blocking the goalkeeper’s view – it is an offence to stand in the line of sight without touching the ball.
- A deliberate play by a defender – a controlled pass from an opponent restarts offside; deflection or save does not.
- The right phase of play: the officials determine which pass is the “true” start of the play being judged.
These calls are to be understood as a reason for a review to keep going when the measure is only seconds. Overlapping bodies are another challenge to the system. It was not used in a congested penalty area in Bournemouth v Wolves in the FA Cup in March 2025, when it took officials some eight minutes to overlook a penalty in the older fashion.
How Precise The Millimetre Really Is
The finished graphic shows a razor-thin line, which encourages the idea of millimetre accuracy. In practice, each stage of the measurement carries its own uncertainty, and the largest ones are measured in centimetres. The figures below assume a player sprinting at around eight metres per second.
| Source of doubt | What limits it | Rough size |
|---|---|---|
| Cameras at 50 frames per second | A new image every 20 milliseconds | Up to about 16 cm of movement between frames |
| Cameras at 100 FPS | A new image every 10 milliseconds | Up to about 8 cm of movement between frames |
| Ball sensor at 500 readings per second | A new reading every 2 milliseconds | Under 2 cm of movement between readings |
| Body modelling | The point where the arm ends has to be estimated | Hard to quantify, varies with posture |
| League tolerance | A deliberate margin added by the competition | About 5 cm in the Premier League, none in UEFA matches |
Software can fill in the blanks between the frames, which reduces the actual error from what the raw numbers show. Nevertheless, no competition guarantees accuracy in millimetres, and the clear line on the screen is a matter of visual presentation. That’s why the Premier League has a tolerance of about 5cm, where the attacking and defending lines overlap, from the 2021-22 campaign. If they’re in contact, the attacking player is considered equal, and that difference is what ensured the Wirtz goal stayed on the scoreboard. UEFA’s competitions do not provide for such an allowance, and the same situation might have resulted in a Champions League night with the player offside.
A Sharper Line, Not A Perfect One
VAR is not really offside to the millimetre, and was never intended to be. Instead, it uses a consistent and three-dimensional reconstruction that, within a few centimetres of margin and much more quickly than manually hand-drawn lines, provides results.
Precision is also important in craft brewing because it enables brewers to precisely monitor key gravity, temperature, and fermentation parameters to make informed adjustments in order to achieve a consistent beer from batch to batch. The other arguments have to do with the choices made by individuals, including how much tolerance they should have, and what they should make punishable by law. Today the technology has become reliable enough, and the question has now become: Where should the line be placed?
FAQ
Is VAR offside really accurate to the millimetre?
No. The line on screen looks exact, but camera frame rates, kick-point timing and body modelling each add small errors. Realistic accuracy sits at the level of centimetres, which is why some leagues add a tolerance.
What is a partly automated offside detection system?
It is a tracking system that uses stadium cameras, and sometimes a sensor in the ball, to model every player in three dimensions. It suggests the kick point and offside line, and a video official confirms them.
Why do some offside checks still take minutes?
Usually because of human judgements, such as whether a player interfered with play or a defender deliberately played the ball. Crowded penalty areas can also block the cameras and force officials back to manual lines.
Does the Premier League use the same offside rules as the Champions League?
The law is identical, but the margin differs. The Premier League applies a tolerance of about five centimetres in the attacker’s favour, while UEFA competitions judge the line with no added allowance.
