kick hit someone when he she is down

idiom
to criticize or take unfair advantage of someone when they are in a weak position
زمین خورده را نمی زنند، از قدیم گفته اند که زمین خورده را لگد نمی زنند
It's typical of the boss to kick someone when they're down

منابع

• https://dictionary.cambridge.org/dictionary/english/kick-hit-when-down