The boys were rough-housing in the backyard and accidentally knocked over a flowerpot.

rough-housing 是由形容词 rough（粗鲁的、粗暴的）和名词 housing（房屋、住所）组成的复合动词，加上-ing 作为现在分词形式。rough-house 原指"在室内粗暴打闹"，现在泛指"嬉戏打闹、玩闹"的行为，通常指孩子们活泼但有些粗鲁的玩耍方式。