To make a sudden and unexpected counterattack or comeback, often after appearing to retreat or give up; to turn around and strike back surprisingly.
他本以为对手已经放弃了追赶，没想到对方突然杀了个回马枪，让他措手不及。
He thought his opponent had given up the chase, but unexpectedly, the opponent made a sudden counterattack, catching him off guard.
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