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Key events can be any memorable event, for example an impressive victory but also a major crash, bold solo or anything that makes for sporting memories.
Just one day after taking the lead in the 1951 Tour de France, Wim van Est fell into a canyon in the descent of the Col d'Aubisque on stage 13 from Dax to Tarbes. He was rescued with 40 tubes tied together. Even though he didn't sustain any major injuries, he dropped out of the race.