a cheap shot

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

coup bas, attaque facile

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.
Son commentaire sur ses erreurs passées était un coup bas.
The politician took a cheap shot at his opponent's family.
Le politicien a fait un coup bas à la famille de son adversaire.