California Codes, Code of Civil Procedure - CCP, Part 2 — Of Civil Actions, Title 6 — Of the Pleadings in Civil Actions, Chapter 2 — Pleadings Demanding Relief, Article 2 — Compulsory Cross-Complaints, Section 426.30
(a) Except as otherwise provided by statute, if a party against whom a complaint has been filed and served fails to allege in a cross-complaint any related cause of action which (at the time of serving his answer to the complaint) he has against the plaintiff, such party may not thereafter in any other action assert against the plaintiff the related cause of action not pleaded.
(b) This section does not apply if either of the following are established:
(1) The court in which the action is pending does not have jurisdiction to render a personal judgment against the person who failed to plead the related cause of action.
(2) The person who failed to plead the related cause of action did not file an answer to the complaint against him.
Notes
Bars a defendant who answers a served complaint from later asserting in another action a related cause of action that existed against the plaintiff when the answer was served but was omitted from a cross-complaint. Exempts cases lacking personal-judgment jurisdiction over that person and cases in which the person did not file an answer.
Use as reference
Lexinter.net | California Code, Code of Civil Procedure - CCP § 426.30 | https://laws.lexinter.net/codes/california/code-of-civil-procedure/part-2/title-6/chapter-2/article-2/section-426-30