The race was the fourth round of the 1982 Formula One World Championship. Its context was already politically charged. Following the 1982 Brazilian Grand Prix, Nelson Piquet and Keke Rosberg had been excluded after their cars were found to have used water tanks as ballast to remain under the minimum weight limit during race conditions while running lighter in qualifying. The Formula One Constructors' Association protested the decision and organised a boycott of the San Marino round.
The FOCA-aligned teams — Brabham, McLaren, Williams, and Lotus — withdrew. However, Tyrrell, Osella, ATS, and Toleman broke the boycott, citing sponsor obligations. They joined the FISA-aligned Ferrari, Renault, and Alfa Romeo teams. The result was a grid of just 14 cars from seven constructors. The boycott left a skeleton field in which Ferrari's dominance would prove nearly total, and in which a team order would become a catastrophe.
René Arnoux and Alain Prost (Renault) qualified first and second. Both retired during the race, handing Ferrari an uncontested front row. Gilles Villeneuve led Didier Pironi, with the third-placed Tyrrell of Michele Alboreto far enough behind that Ferrari issued an instruction to slow down and preserve the cars, minimising the risk of mechanical failure or fuel exhaustion.
Villeneuve interpreted the signal as an instruction to hold position for the remainder of the race, with himself ahead of Pironi. Pironi did not share that understanding. He passed Villeneuve. Villeneuve, believing Pironi was simply playing to the crowd to make the closing laps more dramatic, re-passed him — fully expecting Pironi to settle for second as any teammate would. On the final lap, however, Villeneuve failed to defend the inside line going into the Tosa corner, and Pironi swept through to take the win.
Pironi won. Villeneuve crossed the line second. Alboreto was third. Manfred Winkelhock was subsequently disqualified after his ATS-Ford was found underweight in post-race scrutineering.
Villeneuve was furious. He had understood the team's order as a guarantee of position, not a mutual licence to race. Standing on the podium, his expression was closed and distant. His words afterwards were unambiguous: "I'll never speak to Pironi again in my life."
Inside the Ferrari team, opinion was split over the precise meaning of the slow-down signal. That ambiguity did nothing to cool Villeneuve's anger. He was still not on speaking terms with Pironi when he died during qualifying for the Belgian Grand Prix at Zolder two weeks later, his anguished post-Imola state an inescapable part of the circumstances surrounding his death.
Pironi's overtake on the final lap is regarded as one of the most controversial moments in Formula One, a collision of competing interpretations of team orders that neither driver lived to fully resolve — Pironi himself suffered career-ending injuries later that same season.
Despite the majority of FOCA teams boycotting the race, the 1982 San Marino Grand Prix counted towards the World Championship. This was a source of further contention: two earlier races held during the FOCA–FISA war — the 1980 Spanish Grand Prix and the 1981 South African Grand Prix — had been downgraded to non-championship status after similar boycotts by manufacturer-aligned teams. The inconsistency in how championship status was applied remained a grievance among FOCA members well into the season.