instruction: Based on the information provided, what was the controversy surrounding the 2021 Abu Dhabi Grand Prix?
context: The 2021 Abu Dhabi Grand Prix (officially known as the Formula 1 Etihad Airways Abu Dhabi Grand Prix 2021) was a Formula One motor race held on 12 December 2021 at the Yas Marina Circuit in Abu Dhabi, United Arab Emirates. Contested over a distance of 58 laps, the race was the twenty-second and final round of the 2021 Formula One World Championship. The race decided both the Drivers' and Constructors' championships; Max Verstappen and Lewis Hamilton both had 369.5 points coming into the race. Hamilton led most of the race and appeared on course to win what would have been a record eighth World Drivers' Championship, having taken the lead at the start of the race at turn 1 on the first lap. However Verstappen was the eventual winner, overtaking Hamilton on the final lap after a controversial safety car restart in the last moments of the race. The FIA thus conducted an inquiry into the race which led to a restructuring of race control including the replacement of Michael Masi as race director and amendments to the safety car rules. That inquiry subsequently concluded that the race officials had misapplied the then-regulations due to human error, but confirmed the results.
  
  Verstappen's win secured his first Formula One World Drivers' Championship of his career by eight points from Hamilton, and Red Bull Racing's first since 2013. Mercedes won their eighth consecutive Formula One World Constructors' Championship, setting a new record. The Grand Prix was also the final race for 2007 World Champion Kimi Räikkönen; the 42-year-old Finn retired from Formula One after a two-decade career spanning 349 Grands Prix starts.
  
  Race
  
  Start and opening laps
  The race started at 17:00 local time on Sunday 12 December. Lewis Hamilton immediately took the lead from Max Verstappen on the race start, prompting Verstappen to attempt to regain his position at the turn 6 chicane. Verstappen's trajectory forced Hamilton off the track, and the Briton re-entered slightly further ahead of the Dutch driver than he was before the corner. Arguing that he should have ceded the position to Verstappen, Red Bull Racing protested the racing line taken by Hamilton, and were told by radio that Hamilton had ultimately given back any advantage gained. The incident was referred to the stewards, which concluded that no further investigation was necessary. Hamilton then utilised the durability of his medium-compound tyres to extend his lead over Verstappen, whose soft-compound tyres were suffering from greater degradation.
  
  Pit-stops and virtual safety car
  Verstappen made his stop at the end of lap 13 with Hamilton following suit one lap later, both opting for a set of the hardest tyres. The lead drivers pitting elevated Sergio Pérez to first, with the Mexican driver being informed his strategy was to hold up Hamilton to allow his teammate Verstappen to catch up. Hamilton caught up with Pérez on lap 20; a spirited defence from the Red Bull second driver allowed Verstappen to significantly close the gap from about 11 seconds after the pits to 1.3 second. Verstappen was unable to take advantage of it, with Hamilton's superior pace extending the gap to four seconds by the midpoint of the race.
  
  Final laps
  On lap 53, a crash at turn 14 for Nicholas Latifi, who was fighting for position with Haas' Mick Schumacher and had dirty tyres after going off circuit at turn 9, brought out the safety car. Hamilton again stayed out without pitting because he would have lost track position had the safety car period not ended, while Verstappen pitted behind him for a fresh set of the softest available tyres. Pérez retired under the safety car due to oil pressure. After Verstappen's pit stop, he retained second, but with five lapped cars (those of Lando Norris, Fernando Alonso, Esteban Ocon, Charles Leclerc, and Sebastian Vettel) between himself and Hamilton (in first). As the debris from Latifi's crash was being cleared by the race marshals, the lapped drivers were initially informed that they would not be permitted to overtake. On lap 57 Masi gave the direction that only the five cars between Hamilton and Verstappen were to unlap themselves.
  
  Immediately after Vettel passed the safety car to join the lead lap, race control announced the safety car would enter the pits at the end of the lap to allow for a final lap of green-flag racing, leading to angry remonstrations from Mercedes team principal Toto Wolff. On the final lap, Verstappen used his fresh soft tyres to pass Hamilton into turn 5 to take the lead of the race. He held off counter-attacks from Hamilton to win the race and his first World Drivers' Championship, with Hamilton in second and Ferrari driver Carlos Sainz Jr. in third. AlphaTauri driver Yuki Tsunoda finished in a career-best fourth place, after overtaking Bottas. Mercedes gained enough points to win their eighth consecutive Constructors' title, extending their own record. Over the radio, Wolff appealed to Masi to reinstate the order of the penultimate lap, to which Masi gave the reply: "Toto, it's called a motor race, ok? We went car racing."
  
  Safety car controversy
  Michael Masi was involved in a safety car procedure controversy during the last laps of the race. On lap 56 of the race, during which Hamilton was leading, Masi allowed only the five cars directly in between championship contenders Hamilton and Verstappen to unlap themselves before the restart. The race restarted, and on the final lap of the race, Verstappen overtook Hamilton and won the 2021 World Drivers' Championship.
  
  Mercedes' post-race protests
  Mercedes protested the race result, alleging that Verstappen had overtaken Hamilton during the safety car and that Masi violated safety car procedure by allowing the cars directly in front of Verstappen to unlap themselves, and no others, and that according to regulations the restart should have occurred the following lap, which would have resulted in Hamilton's victory. While the first issue was dismissed because Verstappen was not ahead at the end of the safety car period, the second issue was more contentious, with Mercedes retaining legal counsel for the protest. Mercedes argued that if a message for lapped cars to overtake is issued under Article 48.12, then all lapped cars are required to unlap, and that the safety car was required to wait until the end of the following lap to return to the pit lane; if this process was complied with, Mercedes submitted that Hamilton would have won the race and therefore the championship, and requested that the classification be amended as such. Red Bull argued that a) the regulation stated "any cars", not "all cars", were required to overtake under Articles 48.12; b) 48.13, which governs the withdrawal of the safety car, overrides Article 48.12; c) Article 15.3 gives the race director overriding authority over the use of the safety car; and d) the race result would not have changed if all eight lapped cars were permitted to unlap. Masi argued that the principle behind Article 48.12 was to remove cars which "interfered" with drivers racing on the lead lap and that all teams had agreed in principle that all races should end under racing conditions.
  
  The clerk of the course shall work in permanent consultation with the Race Director. The Race Director shall have overriding authority in the following matters and the clerk of the course may give orders in respect of them only with his express agreement: ... e) The use of the safety car.
  
  
  Mercedes lodged their intentions to appeal the ruling. Following the FIA's announcement that it would conduct a "detailed analysis and clarification exercise" of the incident and its admission that the controversy was "tarnishing the image" of the sport, Mercedes decided not to pursue their appeal, and announced the discontinuation of their protest on 16 December, several hours before the submission deadline. Amongst the reasons to discontinue, Wolff said that neither he nor Hamilton wished to be awarded the drivers' championship in court, and instead would focus their efforts in to ensuring an equitable result from the FIA's investigation into the sporting code. Wolff remained heavily critical of Masi's direction of the race—in particular, Wolff criticised Masi's decision in Abu Dhabi as being inconsistent with a decision at the 2020 Eifel Grand Prix, where Masi cited the need to let all cars unlap to extend a safety car period—and both he and Hamilton boycotted the FIA Prize Giving Ceremony that evening. Hamilton was later fined for not attending; he asked the FIA to donate the fine as contribution towards the work the body carries out with underprivileged children. The statement also fuelled speculation that Hamilton could announce a snap retirement after being disillusioned by the race's events, although Wolff indicated both he and his driver would continue in the sport after a period of reflection in the off-season.
  
  Race reactions and commentary
  In the immediate post-race interview, Hamilton and his father Anthony congratulated Verstappen and his family on his first World Drivers' Championship.
  
  Several drivers criticised Masi's decision which was seen as a divergence from standard safety car procedure. In a last-lap radio message to his race engineer Peter Bonnington, that was not played on the television feed, Hamilton said the race result had been "manipulated". Russell, who was signed to be Hamilton's teammate at Mercedes in 2022, called the race finishing decision of race director Michael Masi "unacceptable". Norris, who was situated at the front of the five cars permitted to unlap, said the decision to go racing again on the last lap was made "for TV", and Alonso, Ocon, Leclerc, and Vettel, the drivers of the other four cars in the pack, also expressed confusion at the sudden instruction to unlap. Daniel Ricciardo, who was situated immediately behind Verstappen during the safety car period and was not permitted to unlap himself, said he was "speechless" at the instruction, especially as it did not allow him to also race the five-car pack on newer soft-compound tyres, and Sainz Jr., who was positioned behind Ricciardo and Lance Stroll's cars upon the restart and was under pressure from Yuki Tsunoda, Pierre Gasly, and Valtteri Bottas, opined that the decision to resume racing under the circumstances "nearly cost [him his] podium". Speaking at Aston Martin's 2022 car launch in February 2022, Lance Stroll described the Abu Dhabi situation as "ridiculous" and that rules should be set in stone before a season starts.
response: While there was a lot of complexity based on the circumstances that occurred, the prevailing controversy with the race was related to the fact that lapped cars were only partially allowed to clear the track. This meant that Max Verstappen was cleared to attack Lewis Hamilton on fresher tyres for the last part of the final lap. Lewis and Max both needed to win the final race to win the championship. This would have been Max's first ever championship or Lewis' record-breaking 8th championship. By allowing only the cars between Max and Lewis, the race director only partially adhered to the rules. This virtually handed the win to Max and Red Bull. While Mercedes immediately protested the decision and final result. Max was awarded the championship.