Our team was flattened by the opponents in the debate competition.

flattened 是动词 flatten 的过去分词形式。flatten 由形容词 flat（平的）加上动词后缀 -en 构成，字面意思是"使变平"，引申为"彻底击败"或"完全压制"的意思。这里用被动语态表示"被彻底击败"的状态。