having been defeated by A university team,my teammates were downcast.这里的完成时的现在分词的被动语态,表示被defeat这个动作发生在后面的动作were downcast之前,这种时间的间隔有强调的意味.而如果写成：defeated by A university team,my teammates were downcast,这里defeated这个动作,和were downcast这个动作在时间间隔上很近,没有强调二者的先后顺序.