Definition
to unexpectedly turn around and launch an attack on someone or something
During the argument, he suddenly rounded on his opponent.
When she feels bullied, she quickly rounds on her aggressor.
The dog suddenly rounded on the child and barked ferociously.
to retaliate against someone who has criticized you
As soon as I gave him my suggestion, he rounded on me with criticism.
She rounded on her colleague fiercely in response to the criticism.
If you attack my work, I will round on you without hesitation.