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Ronnie Ortiz-Magro denies ever wielding a knife against his baby mama, Jen Harley, in their latest alleged domestic violence incident ... and insists he was only out to protect their daughter.

Sources familiar with the matter tell TMZ ... Ronnie is adamant he NEVER picked up or threatened Jen with a knife during their latest domestic disturbance in L.A. ... which required the cops to come out, break down a door and tase him in the end.

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We're told Ronnie only confronted Jen because he was afraid she was trying to take their daughter away from their Airbnb rental home ... which surveillance footage from a neighbor's house seems to support, on the surface anyway.

TMZ broke the story ... Jen looked pretty terrified as she sidled up to the neighbor's home with 1-year-old Ariana in hand, attempting to open the trunk of the neighbor's car.

Play video content 10/4/19 TMZ.com

The neighbor says they saw Jen trying to drop Ariana over a fence, before we're told Ronnie showed up and snatched back the kid ... allegedly striking Jen as well. Things got worse from there as cops showed up, breached the front door to reach Ronnie -- who was holed up with Ariana -- 'cause he refused to come out.

He eventually had to be subdued by taser, and was arrested on kidnapping charges. He was released from custody a short time later.

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This, of course, is just the most recent dust-up between the volatile pair. There's the ashtray-throwing saga, the ransacking tale ... and then the notorious car-dragging episode. None of that is lost on those closest to them either, BTW.