[tóu jǐng xià shí]   

投    阱    下    石    比喻乘人之危加以陷害。

往井下丢石块。比喻乘人之危加以陷害，和成语“乘人之危”寓意相近。

Attack someone who has already fallen from power

投桃之报    投诸四裔    投隙抵巇    投木报琼    投河觅井