Probably the most famous example is Luis Ocana in 1971. He was seven minutes up on Eddy Merckx with a week to go but crashed on the descent of the Col de Mente during a thunderstorm and was unable to continue.
Merckx himself stacked it. Another rider hooked his handlebars before the start of a stage in 75. Merckx fell on his face and couldn’t eat solid food afterwards.
Then a French fan punched him in the gut.
Probably the most famous example is Luis Ocana in 1971. He was seven minutes up on Eddy Merckx with a week to go but crashed on the descent of the Col de Mente during a thunderstorm and was unable to continue.