The controversial clash between Max Verstappen and Esteban Ocon, which put Lewis back in the lead of the Brazilian GP, is not as straightforward as it might have appeared.
Backmarkers trying to pass the race leader are not common occurrences - speed differential being the obvious reason - but it is not unknown, nor is it outlawed by the regulations. Most famously, perhaps, Eddie Irvine, on his F1 debut at Suzuka, passed Ayrton Senna, leading to a post-race punch-up!
Ironically enough, Irvine was then driving for the same team as Ocon, then known as Jordan Grand Prix. As was the case in both situations, it tends to happen when an offset in tyre performance affords the backmarker superior performance temporarily.
Ocon had started 18th after a gearbox penalty. Starting on the mid-range Soft compound tyre, he had completed a long opening stint, to lap 40, allowing him to go onto the fastest red-walled SuperSoft tyre to the end. He pitted out just behind Verstappen's leading Red Bull, which was on the harder, yellow-walled Soft compound tyre.
Key to Red Bull's formidable race pace in Brazil had been benign tyre usage that had seen Verstappen get to almost half distance on his starting set of SuperSofts - deep enough in to allow him to take the Soft for his second stint rather than the slower Medium compound that both Lewis and Valtteri were on after much earlier stops.