knife [sb] in the backv exprverbal expression: Phrase with special meaning functioning as verb--for example, "put their heads together," "come to an end."
informal, figurative (betray)
在…背后捅刀子 zài bèi hòu tǒng dāo zi
阴险陷害 yīn xiǎn xiàn hài
She knifed him in the back by telling the boss his plans.