A closer look at semi-automated offside technology ahead of Premier League debut

Semi-automated offside technology (SAOT) will finally make its Premier League debut this weekend.

Here, the PA news agency takes a closer look at the system.

What is the background to this?

Exactly one year ago on Friday, top-flight clubs voted unanimously to bring in semi-automated offside technology. The intention was to introduce it following one of the three international windows last autumn, but those deadlines came and went as the Premier League conducted further testing.

The system finally made its bow in the FA Cup fifth round, with the tie between Aston Villa and Cardiff on February 28 the first to use it.

It was further tested in three of the four quarter-final ties, before the Premier League confirmed on April 1 that it would be used in its competition from April 12.

Why is it being brought in?

The Premier League says the system will not change the accuracy of decision-making, which has been at 100 per cent this season. However, it is expected to speed up the process – league bosses anticipate shaving 31 seconds off the length of the average offside check.

VARs will no longer need to manually draw offside lines, except in “edge cases” where several players block the view of the ball or other players for the system’s cameras. That contributed to the delays witnessed at the Bournemouth v Wolves FA Cup tie on March 1, where SAOT was in use.

The images generated by SAOT will be available for broadcasters to use and to show on stadium big screens.

An offside decision will be shown with a red line and onside with a green line. A white vertical wall will represent the offside line, with a blue “pulse” on the defender’s relevant body part.

When an attacker is offside, the part of their body which is offside will appear through the white wall and be outlined in red.

How does the technology work?

Up to 30 cameras have been installed in each Premier League stadium, with several capturing footage at 100 frames per second. The cameras track the exact movement of the ball as well as up to 10,000 surface “mesh” data points per player – meaning the technology will track to see if any attacking player involved in the build-up to any incident was offside.

These are then “flagged” automatically in the software to the VAR and SAOT operator.

Why is it only semi-automated?

VARs must still determine that the technology has identified the correct moment when the ball was played (the “kick point”), the correct player and the correct body part.

VARs and referees will still need to rule on subjective offside calls, such as whether or not a player in an offside position was interfering with play, or whether a defender’s touch constituted a deliberate play of the ball.

Does this mean we will see more ‘toenail’ offsides?

Premier League insists the five-centimetre ‘tolerance’ created by the use of thicker lines remains in place, as it has since the start of the 2021-22 season.