'Real Housewives' Star Jill Zarin Suing Pickleball Business Partner Who Sued Her

Jill Zarin is trying to break the serve of a former business partner in her pickleball company ... because she's now suing him after he filed a lawsuit against her first.

"The Real Housewives of New York" alum just filed her own lawsuit against Noah Springer, who she says is an investor who holds a 25% share in her pickleball paddle testing company, Pickle Pro Labs.

In the lawsuit, obtained by TMZ, Jill claims Noah is sinking their ship with his loose lips ... she says he told a sponsored professional pickleball player their paddle would be tested and provided with certification results "in a couple days" ... even though Zarin insists that timeline is way too short given their company's testing standards.

PPL has deals with pro pickleball leagues in the United States and overseas to provide testing and certification services for paddles ... and Jill says PPL's commercial value depends on its reputation for independence, impartiality, confidentiality, and procedural integrity ... all of which she claims Noah threatened with his alleged comment.

Jill claims Noah's shown a broad pattern of conduct where he shares non-public, confidential and commercially sensitive PPL information with pro players, paddle manufacturers, and others outside normal business channels ... and she says she's heard lots of concerns about him.

TMZ broke the story ... Noah sued Jill last month for allegedly cutting him out of the company's earnings and selling PPL's paddle testing device through a new company.

Jill's putting the pickleball back in Noah's court with her own suit ... and she's going after him for damages and wants an order blocking him from disclosing sensitive company info in the future.