countersues
/ˈkaʊntərˌsuz/
verb
- To sue someone in response to being sued by that person; to file a lawsuit against someone who has already filed a lawsuit against you.
- She decided to countersue her neighbor for harassment after he filed a noise complaint.
- After being sued for breach of contract, the company countersues for defamation.
- The landlord countersues the tenant for property damage after the tenant sues for unsafe conditions.