“打败仗”常见的英文表达是 “suffer a defeat” 或 “lose a battle”。
suffer a defeat：强调遭受失败这一结果，语气稍正式，可用于描述各种规模、性质的失败，不仅限于军事战斗场景。例如：The team suffered a defeat in the final game.（这支队伍在决赛中打败仗了/输了。）
lose a battle：更直接地表明在战斗中失利，军事色彩更浓一些。例如：The army had to retreat after losing a battle.（这支军队在打败仗后不得不撤退。）