The finale to the 2021 Formula One world championship was fitting entertainment at the end of an extraordinary season.
On the final lap of the Abu Dhabi Grand Prix, Max Verstappen overtook Lewis Hamilton and crossed the line in first place to become world champion for the first time.
Hamilton had looked on course for a record eighth driver's title until the safety car came onto the track after Nicholas Latifi crashed with four laps remaining.
It led to a thrilling but controversial finish – but should it have been done differently?
Latifi hit the barriers on lap 54 and the safety car was deployed while the track was cleared.
Given Hamilton had been approximately 12 seconds clear in the lead at the time, Red Bull opted to pit Verstappen for fresh tyres in case a late dash for the chequered flag became a possibility. Hamilton stayed out, his team having warned that bringing him in for a tyre change would have given up track position to his title rival.
Discussions were then held between the respective team principals and race director Michael Masi over how the race would be concluded.
Red Bull's Christian Horner asked why cars that had already been lapped were not being allowed to pass the safety car once it was safe, which would have cleared the track between Verstappen and Hamilton and allowed for a last-lap race for the line.
Race Control, having initially declared that lapped cars would not be released, then gave the order for the five drivers keeping Verstappen from the back of Hamilton to pass the safety car.
This meant that, once the safety car left the track, racing could resume for one final lap – giving Verstappen, on far fresher tyres, the opportunity he needed to pass Hamilton and win the race, thereby clinching the title by just eight points.
Shortly after the race, Mercedes lodged an appeal against the result, citing alleged breaches of Article 48.8 and Article 48.12 of the rulebook: the first relates to overtaking under the safety car, while the second concerns the process of releasing lapped cars.
Why was it controversial?
The Formula One regulations for 2021 state: "If the clerk of the course considers it safe to do so, and the message 'LAPPED CARS MAY NOW OVERTAKE' has been sent to all competitors via the official messaging system, any cars that have been lapped by the leader will be required to pass the cars on the lead lap and the safety car.
"This will only apply to cars that were lapped at the time they crossed the line at the end of the lap during which they crossed the first safety car line for the second time after the safety car was deployed. Having overtaken the cars on the lead lap and the safety car these cars should then proceed around the track at an appropriate speed, without overtaking, and make every effort to take up position at the back of the line of cars behind the safety car.
"Whilst they are overtaking, and in order to ensure this may be carried out safely, the cars on the lead lap must always stay on the racing line unless deviating from it is unavoidable. Unless the clerk of the course considers the presence of the safety car is still necessary, once the last lapped car has passed the leader the safety car will return to the pits at the end of the following lap."
The rules do not specify whether the race director may allow only some of the lapped cars to pass, and not all. This is why Michael Masi's decision to release only the cars between Verstappen and Hamilton, allowing for a final lap of racing between the title contenders, has caused such a debate.
What has been said?
Horner told Sky Sports: "We felt hard done by with the stewards at the beginning of the race, but they did great to get the race going again.
"We were screaming at him [Michael Masi]: 'Let them race'. That's what we've been talking about all year and this championship came down to the last lap. A great strategy call to make that pit stop, to take that set of softs, and then it was down to Max to make it happen.
"It's unheard of to leave the cars unlapped. You could see they wanted to get the race going again, and they don't need to catch up the back of the paddock. They made absolutely the right call - difficult circumstances, and they called it right."
George Russell, who will join Mercedes for the 2022 season, said on Twitter: "THIS IS UNACCEPTABLE! Max is an absolutely fantastic driver who has had an incredible season and I have nothing but huge respect for him, but what just happened is absolutely unacceptable. I cannot believe what we've just seen."
Max is an absolutely fantastic driver who has had an incredible season and I have nothing but huge respect for him, but what just happened is absolutely unacceptable. I cannot believe what we’ve just seen.— George Russell (@GeorgeRussell63) December 12, 2021
Lando Norris, the McLaren driver who was one of those allowed to pass the safety car, said: "I'm not too sure what was said from the FIA. At first, we weren't allowed to overtake, as the backmarkers, so if that influenced decisions to Mercedes and to Lewis and that's the reason they didn't do their pit-stop...
"But then the FIA suddenly changed their minds and they were allowed to let us past. That's where I'm not so sure. For it to end like that, I'm not so sure."
Damon Hill, the world champion in 1996, said on Sky Sports: "This is like running a motor race in a way we've not been used to in the past. They've kept us guessing all the time as to which way a decision is going to go. One team who is not going to be complaining about what happened is Red Bull."
Nico Rosberg, who won the 2016 title, said: "First they said you're not allowed to unlap themselves, then they changed that message once they saw it was safe to do so.
"The thing is that in the document it says 'all cars will be required to unlap themselves' and yet they only let those five cars that were between Lewis and Verstappen unlap themselves. That's where Mercedes are asking if it's okay or not. But I guess in the end Michael Masi can decide what he wants, he's the race director."
Jenson Button, the 2009 champion, said: "It definitely went Max's way only letting those five cars past but earlier in the race it sort of went Lewis' way. Michael Masi wants to get them racing, he doesn't want to decide the world championship."