Read this excerpt from "Thank You, Ma'am.”She was a large woman with a large purse that had everything in it but hammer and nails. It had a long strap, and she carried it slung across her shoulder. It was about eleven o’clock at night, and she was walking alone, when a boy ran up behind her and tried to snatch her purse. The strap broke with the single tug the boy gave it from behind. But the boy’s weight and the weight of the purse combined caused him to lose his balance so, instead of taking off full blast as he had hoped, the boy fell back on his back on the sidewalk, and his legs flew up.Which plot element does this excerpt describe?