Befall is an old-fashioned or literary way of saying something happened by chance. Bad luck befalls a heroine who drops her lucky rabbit foot.
When something befalls you, it’s like bad luck falling on you. An earthquake can befall a city. A terrible disease could befall a child. A bolt of lightning could befall a very unlucky person. When something befalls you, you’re in trouble. Tragedies befall families in many of Shakespeare’s plays — that’s what makes them so much fun.