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in Toronto and advanced to the round of 16, leaving Croatia players and fans devastated in the belief Josko Gvardiol's goal was wrongly called offside by the VAR and referee Espen Eskås.

FIFA is relying on a fitted with “advanced sensors” and insisted it got it right when determining Croatia's Igor Mantanovic got the slightest of glances with his head, meaning Mario Palasic was in an offside position during the buildup to the goal.

The in-ball sensors were so finely tuned, FIFA said, they were “capable of determining any slight contact ... allowing officials an unprecedented level of data to make fast, accurate decisions.”

Here's the science bit

The official “Trionda” World Cup ball, manufactured by Adidas, is fitted with a “small inertial measurement unit (IMU) sensor,” which FIFA says operates at around 500Hz and captures data 500 times per second.

FIFA says it can track ball acceleration and granular movements in three dimensions and can detect the exact moment a player makes contact.

The ball technology is combined with in-stadium cameras for tracking data that is transmitted in real time to video assistants.

As well as helping to determine offsides, the touch data can also be used for incidents such as handballs and penalties.

How reliable is it? 

The reason the call was so contentious was because even slow motion replays from numerous angles were visually inconclusive that Mantanovic made contact with Ivan Perisic's in-swinging cross.

That is where reliance on the technology came in. Referee Eskås was instructed by the VAR to review the sideline monitor. Replays showed what FIFA calls a “heartbeat graphic” to indicate the moment the ball was touched and there was a clear spike as it apparently grazed Mantanovic's head.

“No matter how fast the ball is moving or the spin of the ball, you can track it really effectively,” The AP was told by professor Manos Tentzeris from Georgia Tech's school of electrical and computer engineering. "The position of the ball is 99.99% accurate ... you know exactly where the players are, even the tip of a shoe, which sometimes determines if someone is offside or onside."

FIFA also used connected ball technology at the 2022 World Cup, and it was deployed at the most recent men's European Championship in 2024.

Tests were carried out from 2020-22 and the technology trialed at tournaments such as the Arab Cup and the Club World Cup. 

This is not the first time 

The ball sensors also had a decisive impact at Euro 2024 by detecting Denmark's Joachim Andersen handled in the box against host Germany. After a VAR review a penalty was awarded and Kai Havertz scored and Germany won 2-0.

“In my opinion this is ,” Denmark coach Kasper Hjulmand said after his team also had a goal ruled out by VAR.

Those sentiments were echoed by Croatia coach Zlatko Dalić after his team's painful exit. 

“All these decisions take the joy out of football," he said.

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AP sports writer Maura Carey in Atlanta contributed.

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James Robson is at

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