The Basque derby didn't just serve up a controversial penalty. It exposed an unprecedented crisis of confidence at the heart of Spanish refereeing.
Video technology awarded Athletic Bilbao a penalty against Real Sociedad based on a signal from the smart chip inside the ball. Then the manufacturer's own report overturned everything, confirming a technical fault.
That shocking truth prompted former international referee Iturralde Gonzalez to issue a resounding warning: "They have planted doubt in everything."
The incident traces back to the match Athletic Bilbao won 2-1, specifically the controversial moment between Jon Aramburu and Nico Williams that led to the penalty.
Media figure Manu Carreño revealed, on the programme "El Larguero" on "Cadena SER" radio, that the Technical Committee of Referees requested an urgent report from the German company "Kinexon", the firm behind the chip embedded inside the match ball, to establish exactly what happened.
According to Carreño, the committee initially confirmed the penalty was awarded because the ball's signal indicated Nico Williams had touched it last. The surprise came next: the report revealed two peaks in the signal that didn't match the video feed.
In its report, the company admitted a "slight difference in synchronisation, by one or two frames, between the ball's signal and the VAR video". Based on that fault, "the most prominent peak coincides with the moment Real Sociedad player Aramburu reached the ball".
Even so, the referees' committee insisted that "the decision of the VAR room was correct at that moment given the lack of available evidence". It then conceded that "in light of the report's conclusions, the Sociedad player was the last to touch the ball, which could make the penalty decision incorrect".
Planting doubt over La Liga goals
Here Iturralde Gonzalez stepped in to explain the scale of the problem. Given the evidence available to referee Carlos del Cerro Grande at the time, awarding the penalty was understandable. But once the "electrocardiogram of the ball", as he put it, appeared on the screen and a time discrepancy of between 20 and 40 milliseconds became apparent, it was clear Aramburu had touched the ball last and there was no penalty.
More serious still, according to Iturralde, are the repercussions of that admission. With the new chip system, "the machine is the one that captures the frame", and once the company admitted the lack of synchronisation, they had "planted doubt" over the legitimacy of every marginal offside call made since the start of the season.
Iturralde put it sharply: "Are all those goals up to the eleventh round in which marginal offside cases were judged, whether in favour of the team or against it, legitimate? We do not know whether this lack of synchronisation equivalent to 20 or 40 milliseconds occurred only in the Basque derby match or in other matches."
Carreño weighed in too: "It is natural for technology to fail, a human may err and a machine may break down, but we deal with this on a daily basis." That puts confidence in the entire system on the line, especially after Javier Tebas' recent comments.
The La Liga president had called for greater intervention from VAR technology, arguing it should have stepped in on the Mbappé attack. Iturralde responded furiously: "It is unreasonable for the La Liga president to say that VAR should intervene in the Mbappé moment, while just seven minutes before there was a stamping incident by Diomande and it did not intervene, and he seems to have forgotten that completely."
The former referee signed off with a decisive message: "A little respect for the Technical Committee of Referees."