Legal Question in Civil Litigation in California

Your question is too broad and vague. We would have to write a treatise on business torts for you to answer your broad question. You need to narrow your question or go visit your county law library.

California actually recognizes two separate torts: Tortious Interference with Contract and Tortious Inteference with Prospective Business Advantage.

"The elements which a plaintiff must plead to state the cause of action for intentional interference with contractual relations are (1) a valid contract between plaintiff and a third party; (2) defendant's knowledge of this contract; (3) defendant's intentional acts designed to induce a breach or disruption of the contractual relationship; (4) actual breach or disruption of the contractual relationship; and (5) resulting damage." (Pacific Gas & Electric Co. v. Bear Stearns & Co. (1990) 50 Cal.3d 1118, 1126, internal citations omitted.)

The elements of Tortious Interference with Prospective Economic Advantage are "(1) [a]n economic relationship between the plaintiff and some third party, with the probability of future economic benefit to the plaintiff; (2) the defendant's knowledge of the relationship; (3) intentional acts on the part of the defendant designed to disrupt the relationship; (4) actual disruption of the relationship; and (5) economic harm to the plaintiff proximately caused by the acts of the defendant." (Youst v. Longo (1987) 43 Cal.3d 64, 71, fn. 6.)

Venue rules govern where civil actions are filed. The general rule is that venue is proper where a defendant resides, or where the cause of action occurred. But you don't provide sufficient information to determine which cause of action applies, and whether special venue rules apply.