What is semi-automated offside technology and how does it work? – The Athletic

As Victor Torp sprinted toward the Wembley corner flag and fell onto his back, Coventry City looked like they had produced one of the greatest moments in FA Cup history.

Having been 3-0 down against Manchester United after 70 minutes, they had pulled off a remarkable comeback to lead 4-3 in stoppage time of extra time.

More than 36,000 Coventry fans were in euphoria and some Manchester United supporters left the stadium. The noise was deafening but then came the silent wait for the VAR.

But 118 seconds after Torp had put the ball past Andre Onana, the goal was chalked off for the tightest of offsides as Coventry forward Haji Wrights toe was judged to be slightly beyond Aaron Wan-Bissakas toe.

Championship side Coventry went on to lose 4-2 0n penalties, missing out on what would have been just their second FA Cup final appearance, having won it in 1987.

It led to widespread outcries on social media about the delay diminishing Coventrys outpouring of emotion but also doubt being cast over the accuracy of the VARs call.

From next season, the Premier League will have technology that should see these gripes consigned to history: semi-automated offside technology (SAOT).

It is yet another acronym that fans will have to get used to after Premier League clubs unanimously approved the use of SAOT for the 2024-25 season, which is estimated to be available for use after one of the autumn international breaks.

Despite being in its fifth season, complaints about the time delays when the VAR has to study marginal offside calls still exist. In that context, the addition of SAOT feels like an important step.

The Premier League believes it will save an average of around 31 seconds per offside and there is the bonus of officials being instantly informed of the decision via an earpiece, which means an assistant referee can raise their flag as soon as they hear, rather than having to wait on the phase of play to come to an end.

But how does SAOT work?

The answer is: it depends. There is more than one path that leagues and competitions can take when implementing SAOT.

FIFA and UEFA use Hawk-Eyes SAOT technology but FIFA uses the connected ball add-on. Both require a camera-based optical skeletal tracking system, which uses video cameras to monitor around 30 joints on each players body.

The cameras automatically pick these up like antennas as soon as they go onto the pitch and its algorithms constantly calculate whether an attacker is in an offside position.

But the major difference between the two is that the latter uses the connected ball and the Premier League does not intend to use that.

Munich-based Kinexon is the company that worked in conjunction with FIFA and Adidas for five years to produce 1,500 of these high-tech footballs for the mens 2022 World Cup and 1,500 for the 2023 Womens World Cup.

After its success, it will do the same for the mens Euro 2024 and womens Euro 2025 match ball called Fussballliebe German for love of football.

Our in-ball chip is an advanced add-on for SAOT, says Daniel Linke, product marketing and strategy lead at Kinexon.

Using only an optical-based system has a greater error margin due to the shutter time of the camera, motion blur, picture angle and resolution.

The standard broadcast cameras (used by VAR) record at 50 frames per second but Kinexons in-ball chip can judge when the ball has been touched 500 times per second.

With VAR in its current form, there is contention about whether the picture was frozen on the correct frame for offside calls eg, working out the exact moment the ball had left Callum OHares boot for Coventrys disallowed goal on Sunday but this is where Kinexons in-ball chip can offer a more precise judgement.

Weve all watched games with VAR where play is interrupted and they spend five minutes looking, only to draw the wrong conclusion, says Linke.

Its so tricky to see from the video images exactly when the ball is touched as the picture might be blurred or occluded. With our connected ball, you get that information instantly. It is in perfect synchronisation with the video signal; we have it down to one or two milliseconds.

Then the camera systems algorithms are constantly working to assess offside every time a touch signal is sent by the ball chip.

Linke talks to The Athleticthrough one of FIFAs example videos, which shows how the chip complements the cameras to provide virtually real-time offside calls.

What you see in red is the touch signal, he says. There is a peak when the ball is touched and that means you can see the picture instantly.

Every line you see is a frame. When we detect a touch we send this to the VAR software. Between two picture frames we have 10 data points from the ball whenever there is a touch, so when you see the video with the touches overlayed you click on the image and the line is drawn instantly on the correct frame.

That high-resolution sensor allows it to detect a full-strength kick to a subtle graze undetectable to the naked eye.

The chips other strength is that the sensor has an inertia measurement unit inside, which is basically an accelerometer, he says.

It has a high-resolution touch signal so every time you kick it or a feather drops on it, you will see it. Its critical for the offside technology.

You can also tell when the ball has been touched but also ifit has been touched. There was the example of Cristiano Ronaldo when he claimed he headed it but the technology proved he had not. They do it with sound in cricket (snickometer) but the idea is similar.

Domestic leagues typically wait for the International Football Association Board (IFAB, the body that oversees the laws of the game) and FIFA to deploy new technology before it cascades down the football pyramid. FIFA trialled SAOT in the 2021 Arab Cup and Club World Cup before using it for the Qatar World Cup.

Its success meant it was retained for the 2023 Womens World Cup, while Italys Serie A has used SAOT for the past 18 months.

Spains La Liga announced last October it will introduce SAOT from the start of the 2024-25 season but how long before it is almost universally used like VARs?

There are other ball providers following (Adidas) but it takes a year of research and development to find the best way to implement the sensor. You need to design it in a way that it does not affect the physics of the ball.

A lot of testing is required to prove the concept is fail-safe and that the technology does not impact the games aesthetics. The nightmare scenario would be for a player to take a throw-in and hear the chip rattling around.

SAOT is generally less expensive than VAR because less manpower is needed to operate the system. It is fully automated and can be overseen by one operator, whereas VAR requires several people to manually find the right frame and apply the offside lines.

Could there be a double benefit of the chip helping to determine whether the ball is in play or not?

There have been two goals this season when blindspots in VARs camera inventory have been exposed. Unfortunately for Arsenal, both incidents (against Newcastle United and West Ham United) went against them.

VAR has access to all broadcast cameras but the number in operation varies across each match, so there is no uniformity across all 20 stadiums.

Hawk-Eye is the provider of goal-line technology and normally places cameras at the back of the stands or on the roof. Contrary to popular belief, no cameras are placed inside the goalposts or crossbar, so Hawk-Eyes ability to triangulate the balls position to within an average of three millimetres in goal-line decisions is not applicable further along the byline.

We had the same question in the World Cup with the Japan goal that people thought had gone out, says Linke.

People were asking us why we didnt use our technology, but to determine whether the ball has crossed the line or not it needs to be sub-centimetre accurate.

Our strength is in the refresh rate of when the ball is connected with. We can determine the position of the ball but it would only be accurate to within two, three, four or five centimetres.

(Top photo: Ed Sykes/Sportsphoto/Allstar via Getty Images)

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What is semi-automated offside technology and how does it work? - The Athletic