Imagine this on Saturday morning (Singapore time). It's the 89th minute of the World Cup Group B clash between Portugal and Spain at the Fisht Stadium in Sochi, Russia.
Cristiano Ronaldo is felled in the penalty area by David de Gea. Or has he? It all happened so quickly. The referee gulps nervously and traces a box in the air with his fingers. This means VAR (video assistant referee). And VAR could mean chaos.
This summer, for the first time in the World Cup's 88-year history, referees will be able to call upon video assistance for contentious decisions.
Hypothetically, the move should help eliminate mistakes from the game. But VAR is not foolproof and early experiments in some of the world's major leagues have created growing anxiety at what might come to pass in Russia.
Could the biggest tournament in world football be ruined because of computer glitches?
Take the aforementioned hypothetical example of Ronaldo tumbling over de Gea.
Can video replays ever provide conclusive evidence of a contact foul? If they can, then why do pundits and fans around the world continue to debate decisions, even after reviewing them dozens of times from multiple angles?
Even with a clear line of sight, it can be impossible to ascertain the truth.
Fifa president Gianni Infantino has argued that the new technology will have a positive impact on football.
"From almost 1,000 live matches that were part of the experiment, the level of accuracy increased from 93 per cent to 99 per cent," he said.
And yet there were moments this season when VAR failed to convince.
In February, Manchester United were denied a goal by VAR for an alleged offside, "proved" by a wobbly yellow line that seemed to have been drawn around Juan Mata.
VAR: Highs and lows
• Leicester City v Fleetwood Town (FA Cup 3rd round replay, Jan 16, 2018)
Statistics show the VAR does get some decisions right. This was the case with the first goal it awarded in English football. Leicester were 1-0 up by the time Kelechi Iheanacho tucked home a Riyad Mahrez pass in the 77th minute. He was initially adjudged offside but VAR checks all goals scored and confirmed that Iheanacho was actually onside thanks to defender Nathan Pond's foot.
• Cameroon v Chile (Confederations Cup, June 18, 2017)
One early VAR test came in Moscow. Chile's Eduardo Vargas' first-time finish was retrospectively ruled out for a marginal offside on the stroke of half-time. Forty-five minutes later, the technology put Vargas on the scoresheet; it overruled an offside decision against Alexis Sanchez, whose parried effort Vargas had turned into the net.
• Tottenham v Rochdale (FA Cup 5th round replay, Feb 28, 2018)
Trials in England have been such a mixed bag that Premier League clubs in February opted out of implementing the technology next season, and this game might well have featured in their thinking. Spurs had a decent effort overturned by the technology and were then awarded a penalty that probably was not. Both decisions also took an eternity to process, which was inconvenient for the crowd at Wembley, as the match was taking place in sub-zero temperatures due to a blizzard.
• England v Italy (International friendly, March 27, 2018) See graphic.
What they say
Fifa deputy secretary-general Zvonimir Boban
"The philosophy of VAR is that we are searching for more fairness in the game. Everything at this Fifa World Cup will be shown on screens in the stadia: footage, clear wording. In terms of communications, this will mean a lot for the fans."
Pierluigi Collina, chairman of Fifa's referees committee
"It's not a question of refereeing the match with technology. The goal has never been to check every minor incident. It's about avoiding clear and obvious major errors."
Gareth Southgate, England coach
"In general, it's (VAR) the right route to go but I prefer that the referee's decision is final. It must be clear and obvious - otherwise it's just opinion again - and there must be a better way of communicating with the fans. There's a clearer communication with those in the stadium in other sports."
In Germany, a referee was forced to recall Mainz and Freiburg players from the dressing room at half-time to take a penalty that hadn't been noticed when they were on the pitch.
In Australia, a "malfunction of software", meant that a crucial and evidently offside goal in the A-League grand final was missed, although in this case the human officials missed it too.
And while it's one thing for the television audience to enjoy the mounting tension created by VAR, the reality in the stadium is very different.
Without the communication enjoyed by sports like American football, supporters can be left baffled by unexplained events on the pitch.
There was widespread derision from the Wembley crowd in February when Tottenham Hotspur's FA Cup replay with Rochdale was repeatedly delayed by consultation between the referee and his team.
And this was a one-sided game with relatively little pressure. Imagine how the crowd might react in a tense knockout game.
Fifa has promised to develop a VAR information system to ensure that "a Fifa staff member informs the broadcasters, commentators and infotainment about the different steps of the review process", which include "VAR-specific graphic templates for TV and the giant screen in the stadium".
But, in the cauldron of an excitable football stadium, that may not be enough.
Spurs manager Mauricio Pochettino, speaking after that odd night at Wembley, is one of many who believe that the referees, and their human weaknesses, are just part of the game.
"My opinion is that we have the best referees in Europe," he said. "The referee is the boss on the pitch and has the last word always."
Not now, he doesn't. And all of football will have to hold their breath and hope that VAR doesn't go horribly wrong in Russia.
• Iain Macintosh is a football writer and broadcaster. Formerly with ESPNFC, he can be heard on the The Totally Football Show podcast, available on iTunes.