fight back
To act in one's self-defense, either verbally or physically. If that bully confronts you again, you need to fight back. They were tearing my story to shreds—I had to fight back!
fight back (at someone or something)
to defend oneself against someone or something; to retaliate against someone or something. You are going to have to fight back at them. You can't expect us to defend you. It's hard for me to fight back against three of them by myself.