放冷箭，中文俗语，“冷箭”同“暗箭”，表示“an arrow shot from hiding”，放冷箭指“乘人不备，放箭伤人（to shoot at someone from a position where you cannot be seen）”，比喻“暗中伤人”，英文可以翻译为“stab in the back”，或“resort to underhand means”。
It is easy to dodge a spear in the open, but hard to guard against an arrow shot from hiding.
Harman claimed she was the victim of backstabbing by jealous colleagues.
They told me they would back me up. But as a matter of fact, they stabbed me in the back.