A man waved a cloth and another man died. Why?
Answer 1: The man waving the cloth was announcing the start of a duel. As soon as the cloth was waved, the fastest of them shot the other man down.
Answers which came out of all the comments the readers left:
Answer 2: The man waving the cloth was a station master and when he waved the cloth (a flag, if you insist on the right term) the train started and a man standing on the tracks died a gruesome death.
Answer 3: A man waving a piece of cloth was the signal for a firing squad to shoot down the man standing in front of them.
Answer 4: Here is the bullshit-est of all the answers. A man standing behind a matador in a bull ring waves a cloth and enrages the bull. The angry bull attacks the matador when he is not looking and kills him.