drop stones on sb who has fallen into a well—hit (/kick/strike) a person when he is down; add to the misfortunes of a man who is already unfortunate; add insult to injury ❍ 他甚至对同志有害人之心，“～”，利用同志的弱点和困难去打击和损害同志。(刘少奇《论共产党员的修养》51) They even scheme to injure comrades，“drop stones on one who has fallen into a well，”and take advantage of comrades’weaknesses and difficulties to attack and harm them.
落井下石luo jing xia shi
drop stones on someone who has fallen into a well—hit a person when he's down
落井下石
drop stones on someone who has fallen into a well (hit a person when he’s down); hit an underdog
落井下石luò jǐnɡ xià shí
有人落在井里，不但不去相救，反而向井里投石头。比喻乘人之危时，不去帮助，反而加以陷害。leave sb. the bag to hold, hit a person, when he’s down, pour water on a drowning man