The Premier League spent two years testing a number of artificial intelligence-based semi-automated offside technology (SAOT) providers, and now it’s ready to be rolled out.

UEFA was first to introduce SAOT in the Champions League from the start of the 2022-23 season group stage, quickly followed by FIFA for the World Cup in Qatar.

SAOT will be make its debut in English football this weekend in the FA Cup fifth round, featuring in the seven ties which are being played at Premier League grounds (stream all eight FA Cup matches this weekend LIVE on ESPN+ in the U.S.).

What is this new technology, how does it work, and is it really any better?

Why does VAR offside need to change?

Long delays, perceived inaccuracies and a lack of confidence in the system among fans, players and coaches. And that’s just for starters.

Scepticism also comes from the poor visualisation of decisions, with lines placed on the pitch that cannot replace a person’s own perspective of an offside decision on a camera angle. A player may look onside, but the technology says they are offside. At other times, the lines are so close to each other it’s hard to understand the outcome.

Selecting the exact point the ball is touched by the passer cannot be determined accurately because of the frame rate of TV cameras (50 frames per second).

The VAR manually selects the farthest forward point on both defender and attacker (or the ball if applicable), which cannot be applied consistently or accurately. Then there’s the time it can take to judge offside, in some cases up to five minutes for complex decisions, and that adds further frustration.

Some grounds cause more trouble than others, too. Offside has proved particularly troublesome for the VAR at Selhurst Park, where it took over four minutes to confirm a Crystal Palace goal earlier this month.

All in all, supporters don’t really trust the process as it works now — not helped by a number of high-profile errors either.

In February 2023, the VAR failed to identify that a Brentford player was offside in the buildup to a goal at Arsenal. On the same day, the lines had been placed on the wrong Crystal Palace defender, leading to a Brighton & Hove Albion goal incorrectly being disallowed.

And in October 2023, Liverpool had a goal ruled out for offside on the field at Tottenham Hotspur which the VAR mistakenly failed to correct. However, the error on the Luis Díaz goal was primarily around communication rather than the technology — an issue SAOT would not be able to fix by itself, but one that a less complicated process may help to prevent.

So what is semi-automated offside technology?

Developed by technology company Genius Sports, the Premier League says it creates a “more efficient placement of the virtual offside line” by taking the mapping of the relevant players out of the hands of the VAR and into the control of technology.

Rather than a referee placing lines onto a 2D TV screen, SAOT will plot the players in 3D.

It will also bring an “enhanced in-stadium and broadcast experience for supporters.”

What is it going to look like?

This is as important as any other part of this project. It was incredibly difficult to visualise offside decisions, and now fans will effectively be moved almost in line with the assistant referee to show an offside.

Much like goal-line technology, a 3D animation is created that will be shown at the stadium and on TV. The animation will also be posted on the @PLMatchCentre X account.

The exact point on the attacker which is deemed offside is highlighted, and a simulation will create a “wall” indicating the offside line. If a player is offside, the relevant part of the body will break through that “wall.”

Unlike with SAOT used in other leagues, the animation will not move directly in line with the two players as that can obscure the decision and be as confusing as the old tech.

It will be far easier to understand for supporters at the ground or watching on television, and like fewer delays should lead to less criticism.

This can take several minutes in the Champions League, as the visualisation is overlayed onto the TV coverage. In the Premier League and the FA Cup, it will be standalone so should be much quicker.

How does SAOT work?

There will be 30 bespoke cameras installed under the roof of the 20 Premier League grounds — or for the purposes of this weekend the seven top-flight stadiums hosting FA Cup games.

These cameras provide optimal tracking for the ball and all 22 players, recording 10,000 surface “mesh” data points per player on all limbs and extremities that are relevant for an offside decision — including the upper arm, toes, knees and head — so the system knows the exact position of a player at any given moment. An offside player can be automatically “flagged” in the SAOT software.

Data will be captured at a rate of 100 frames per second — double the 50 frames per second used in the current offside technology.

All player and ball data is processed in real time, which triggers an alert to the VAR. The VAR must then validate that the kick point and offside line are accurate, and the offside player is active, and then inform the referee who can confirm or change the on-field decision.

The referee will still have to go to the pitchside monitor if there is a subjective offside decision (for instance an attacker in the goalkeeper’s line of sight) to be changed.

Why is SAOT better?

Accusations of human error — sometimes founded, others more conspiracy theory — have always dogged VAR and offside. By taking the process out of the hands of the VAR and into the control of software, accusations of operator bias can be put to bed.

So, how is that achieved? SAOT automates the mapping process and produces a result much more quickly. It removes all subjectivity from this part of the process, and the average time taken for an offside VAR review will be cut by 30 seconds.

The Premier League also believes that SAOT will increase confidence in decision-making by reducing the reliance on manually checking all potential offsides — therefore reducing the likelihood that a potential decision is missed by VAR.

It’s semi-automated because the VAR still has to confirm the result, and the technology cannot tell whether an attacker is actively involved in play or confirm the ball was touched by a teammate of that player.

The VAR will also have to validate the kick point, because there is no chip in the ball in the Premier League version of the technology.

Still, time taken definitely erodes confidence. So, if SAOT can make everything noticeably quicker we might at least lose one of VAR’s areas of criticism.

Why isn’t there a chip in the ball, and does it matter?

The beauty of the chip in the ball is it gives undeniable accuracy over the play of the ball. But Adidas, the provider for FIFA and UEFA, developed the original SAOT and it owns the patent for how the chip sits in the centre of the ball to ensure reliability.

That patent means any other ball manufacturer would need to find a new way of balancing a chip without infringing the Adidas patent. As no top European league has a contract with Adidas, they’ve had to develop their own software.

Without the chip, it has to work slightly differently. SAOT will suggest a kick point to the VAR and automatically create the offside line to that frame.

Tony Scholes, the Premier League’s chief football officer, said earlier this month that he doesn’t believe the lack of a chip will be a problem.

“We believe we’re going to be adopting the best system and the most accurate system without the need for the chip in the ball,” he insisted. “We believe it to be the most accurate and the most futureproof system as well and that’s why we went with that.”

Between the frames, optical tracking is able to interpolate the player and ball movements with the system providing a continuous flow of data.

Right now we only have the official line to go on, the proof will come when we see it in action — the Premier League has certainly done plenty of testing.

More accurate? So more offside goals, and “toenail” decisions?

This is good news, because the Premier League is going to retain the existing “tolerance level,” sometimes referred to as “thicker lines,” which gives a “benefit of the doubt” to the attacker of around 5cm.

It was introduced in 2021-22 after complaints about those so-called “toenail” calls where you can barely tell that a player is offside.

This isn’t in place in the Champions League, LaLiga, Serie A or FIFA competitions, as seen in the image below from the World Cup, which produced some extremely marginal SAOT offside decisions.

If the Premier League had removed the “tolerance level” we’d definitely have seen more goals disallowed, as there are many across a season which fall into this category.

However, if English football is keeping it, that might suggest that the Premier League isn’t yet totally happy with its accuracy. The whole point of the “tolerance level” in the old technology was to compensate for the inaccuracies and inconsistencies.

So, in English football, we won’t be going back to the incredibly tight offside calls we saw when VAR was first introduced. However, there will always be the marginal point when onside becomes offside — you cannot change that whatever system you have.

Will there still be any long delays for VAR checks?

Longer delays should be rarer, because SAOT means the VAR won’t have to go through the manual process of mapping the players.

However, there will be occasions when there are subjective elements to a decision. Is a player interfering with play? Has there been a “deliberate play” of the ball by the defender? Is an attacker in the line of vision of the goalkeeper? Those decisions, and others with multiple offside elements, will take longer.

There will also be situations where players block each other in the system’s cameras, or there may be multiple checks in one phase.

For instance, there was an offside check in Everton vs. Manchester United earlier this month which took over three minutes, and SAOT would not have improved that as it wasn’t just related to player positions.

Added to that, as this is new technology the Premier League wants decisions to be checked rather than taken on faith, only for a mistake to be found.

Even in the Champions League with a chip in the ball, there can still be lengthy delays.

Will SAOT be used for all offside decisions?

No, so it’s still possible for a corner to result from a missed offside.

The VAR will only activate SAOT in one of the match-changing moments covered by VAR — goals, penalties and red cards.

What about the delayed offside flag?

While it’s true SAOT can work out player positions quickly, as its only for use on VAR reviews we haven’t seen the end of the delayed offside flag.

Play will still continue in an attacking situation until the end of the phase, when the assistant will raise their flag.

So this is the FA Cup. When will we see SAOT in the Premier League?

Premier League clubs unanimously voted to introduce semi-automated VAR offside technology for the 2024-25 season almost a year ago.

It was supposed to come in after one of the international breaks at the end of 2024, but problems with testing meant it was further delayed.

“We are still testing it, but we are making significant progress,” Scholes added. “We’re in a different place to when I spoke to managers just over Christmas, we’ve made a lot of progress in this area.

“Now I’m hopeful that at some point this season we will be able to introduce semi-automated technology but I repeat the points I’ve made a number of times. We are not going to introduce it if we’ve got any doubts at all with regards to its operation.”

Shortly afterward the FA, the Premier League and PGMOL announced a joint agreement to trial it in the FA Cup.

It could yet feature in the Premier League in the final weeks. Scholes also defended the prospect of switching from the legacy VAR offside technology to SAOT when the majority of the season will have been played.

“It’s a very fair question and we’ve sort of questioned ourselves about this,” Scholes admitted. “But fundamentally, the operation of semi-automated offside technology does not change the integrity of the offside law and doesn’t change the integrity of the decision making.”

However, you have to feel that testing the FA Cup for the rest of the season and launching in the Premier League next season makes more sense. After all, there’s only 11 rounds of fixtures remaining.

Is SAOT in any other leagues?

Serie A was the first European domestic league to switch to SAOT, introducing it in January 2023 after a high-profile VAR error early in that campaign had seen a stoppage-time winning goal for Juventus incorrectly disallowed. Mexico’s Liga BBVA MX also introduced it in January 2023, and it has been used in the CONMEBOL Libertadores, South America’s equivalent of the Champions League.

LaLiga brought in SAOT at the start of the 2024-25 season.