原文地址

kick sb when they're down

落井下石

to continue to hurt sb when they are already defeated
在某人已经被打败的情况下，依旧伤害某人

Don't kick a man when he is down.
不要落井下石。

They're kicking us while we're down because none of us belong to their union.
他们对我们落井下石，因为我们谁也不属于他们的工会。