Barcelona endured only their second La Liga defeat of the season after a shock 1-0 loss at Real Sociedad on Sunday.
After a streak of seven straight wins in all competitions, Hansi Flick's side fell to forward Sheraldo Becker's decisive first-half effort.
But the big talking point from the game was not the end of Barcelona's run or the absence of teenage star Lamine Yamal, instead VAR stole the show with a controversial call to rule out a Barcelona goal when the game was goalless.
How a technical fault from VAR denied Barcelona a goal against Real Sociedad
The controversy at Sociedad arrived in the 15th minute, when Robert Lewandowski had the ball in the net, converting smartly from Frenkie de Jong's pass.
However, as with every goal in the league, it was checked by VAR. Unlike in the Premier League, Spain's top tier use the semi-automated offside technology regularly seen in the Champions League.
After review, the officials chalked off the strike, with the freeze frame provided by the VAR ruling Lewandowski's goal out, the Pole's right boot fractionally offside.
However, when looking at a normal replay of the incident it is clear that Lewandowski remained behind Real Sociedad's Nayef Aguerd - and therefore onside - when the ball was played.
The image used by the VAR came from a particular angle where Lewandowski's boot was not visible.
Instead the line was drawn from Aguerd's boot, meaning the Barcelona striker was onside and the goal should have stood.
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Naturally Barcelona were left furious after the game, with manager Flick saying: "There was no offside. It was not his [Lewandowski's] foot. But we have to accept it.
"Of course, if it were 1-0 to us [if the goal stood], it will have been a different match. But it was different, and it was not our day."
FourFourTwo's verdict is that while semi-automated offside technology should, in theory, significantly reduce the chance of an error following a VAR review, the Lewandowski incident shows the system is not entirely failproof.
Unique perspectives provided by certain camera angles can occasionally lead to an issue with the technology. We have seen this before with Hawkeye's goal-line technology, which managed to produce an error for the first time in 9,000 matches back in 2020 when Aston Villa met Sheffield United in the Premier League.
Villa goalkeeper Orjan Nyland caught a free-kick and accidently fell backwards carrying the ball over the goal-line. But that day referee Michael Oliver did not receive a signal to indicate a goal - as all the cameras were momentarily blocked off, either by the goalkeeper, defender or post.
La Liga have yet to publicly respond to the incident, which helped inflict a second defeat of the season on the league leaders. Despite the defeat, Barca still lead Real Madrid by six points going in the international break.
