I've seen it happen while watching Paris-Roubaix Bicycle Race on TV, in the late '80s. 2 riders escaped from the pack, all alone and approaching the finish line. Each watching the other trying to figure out a tactic to beat the other, when a small plastic bag blew into one's rear derailluer, leaving him stuck in the gear he was in (not the gear he would choose to do the final sprint in), sealing his fate. When the sprint started to the line, his now fixed-gear-bike was no match for the other rider who wound up a gear or two higher, to easily take the victory.