a cheap shot

US /ə tʃiːp ʃɑt/
UK /ə tʃiːp ʃɑt/
"a cheap shot" picture
1.

卑劣な一撃, 安っぽい攻撃

an unfair or unsporting remark or action, especially one made against a vulnerable person or at an opportune moment

:
His comment about her past mistakes was a cheap shot.
彼女の過去の過ちについての彼のコメントは卑劣な一撃だった。
The politician took a cheap shot at his opponent's family.
その政治家は対立候補の家族に卑劣な一撃を与えた。