The Premier League will speed up offside calls with optical tracking tech starting next week

England’s top-tier soccer league will soon use optical tracking to automate portions of offside calls. The Premier League said on Tuesday it will adopt semi-automated offside technology (SAOT) in live matches beginning on April 12. The league said the new tech won’t change the accuracy of offside calls, but it will make them 30 seconds faster on average.

SAOT uses sensors from up to 30 cameras mounted high above the field in each Premier League stadium. They track the ball’s precise location and up to 10,000 surface data points for each player. The sports tech company Genius Sports explains that the tech “provides more efficient placement of the virtual offside line, using optical player tracking, and generates virtual graphics to ensure an enhanced in-stadium and broadcast experience for fans.”

For the uninitiated, offsides is called in soccer when the attacking team’s lead player is closer to the opponent’s goal line than both the ball and the second-last defender. (The last defender is usually the goalie.) In recent years, the Premier League defaulted to the offsite Video Assistant Referee (VAR) team, which would determine the kick-point (the moment the lead attacker’s teammate passes it) and add calibrated lines with a crosshair for the attacker and defender’s locations at that time.

SAOT cuts a big chunk out of this (often lengthy) process by suggesting the kick-point and automatically creating offside lines based on the relevant defender and attacker’s positions. The VAR team still has a chance to review the algorithm’s suggestion before approving it.

At that point, a “decision visual” like the one below will roll for the fans in the stadium and those watching the broadcast at home to help clarify the call. The animation shows a white vertical wall representing the offside line, with a red (offside) or green (onside) line indicating whether the player crossed it.

VAR will still be available as a backup for offside calls. “Most offside decisions will be quicker, but VAR will still have the option to draw crosshairs as a backup to the SAOT system if required,” the Premier League explained. “This process may be necessary in ‘edge cases’ where several players block the view of the ball or other players for the system’s cameras.”

This isn’t the first use of the tech. The Premier League has tested it in non-live matches and in live FA Cup games. The BBC notes that SAOT was also used in the 2022 World Cup, Serie A, La Liga and the Champions League. The Premier League’s version is a custom offshoot that Genius Sports developed with PGMOL (the referees’ organization) and the league itself. Unlike previous adaptations, the Premier League’s version doesn’t put a chip inside the ball.