Supposedly infallible, the system developed by Hawk Eye Innovations minimizes human error to a bare minimum.
SAOT, which stands for Semi-Automated Offside Technology, is the latest buzzword in Football, debuted this season in the league. It is the newest application of technology aimed at resolving offside controversies (or generating even more); a sort of revealed truth through imagery and computing, without human intervention. A supposedly flawless method that shouldn’t leave much doubt. But that is not the case.
What exactly is semi-automated offside? It is a technology that enables the instantaneous determination of whether a player is in an illegal position in offside cases. This technology, termed limb-tracking, utilizes 3D recreation to ascertain the positions of players. It began trials under FIFA in 2021 during the Africa Cup and the Club World Cup, and also featured in the 2022 World Cup in Qatar. It was officially implemented from the 2023-24 Champions League season onwards.
This technological system, developed by Skeletrack, a brand of Hawk Eye Innovations (the only one licensed by UEFA and FIFA), has been utilized in sports since 2018, boasting a track record of over 32,000 matches across football, baseball, basketball, American football, and ice hockey. As the sole provider accredited by FIFA, it was the company awarded the contract by the Royal Spanish Football Federation (RFEF) in January for four seasons, running from the current one until 2027-28, applicable in official First Division matches (and in Second Division from the 2025-26 season). The cost of the system is set at 5 million euros.
How does the offside detection system work? To determine the exact position of a player on the field, the Skeletrack system captures 29 monitored points on each player’s body—”one of the most important being the tip of the toe,” according to Iturralde González—allowing for real-time 3D visual representations. This point capturing is made possible by 10 to 12 cameras installed in the stadiums’ rafters—operating independently from the TV broadcast cameras—providing up to 50 shots per second of each player.
Additionally, the system also accounts for the ball, which sends 500 signals per second, helping to identify the precise moment the boot makes contact with the ball in the final pass. This functionality is enabled by an Inertial Measurement Unit (IMU) sensor installed within the ball itself.
Thanks to this technology, the VAR room referees can determine whether there is offside in a matter of seconds, averaging 25 seconds from the moment the incident occurs. The workload for them is minimal: VAR referees only need to find the exact frame that aligns with the first contact with the ball during the pass action. The system automatically draws the lines of the attacker and defender and recreates the image in 3D for spectators.
But why is it called semi-automatic? The system is “semi-automatic” because it requires a final verification from the VAR room referees before informing the on-field referee. In case of doubt, the VAR referee can adjust the exact moment of the ball strike or the offside line generated by the technology.
SAOT vs VAR
The main advantage of the semi-automatic offside system is its speed and automation, considerably reducing the human factor. Reviewing an offside call using VAR (Video Assistant Referee) can take over a minute (70 seconds, according to FIFA), whereas SAOT reduces this time to about 25 seconds. Furthermore, semi-automated offside minimizes the risk of human error as it provides exact data collected accurately through monitored points of the body and the ball, while in VAR, the video referee team manually selects the ball strike point and draws the offside line. In SAOT, the VAR referee only needs to validate the suggested decision by verifying the automatically created offside line.
