L.A. Dodgers star Yasiel Puig is adamant he never laid a hand on his sister at a Miami bar last week ... claiming they did get into an argument, but things NEVER got physical.
Puig's good friend Alex Vega tells TMZ Sports he was with Yasiel that night and admits things got heated between the Puig siblings, but Yasiel swears he never touched her.
As we previously reported, bar staffers tell us the entire incident was captured on surveillance video -- and it shows Yasiel slapping his sister's hand and pulling her hair.
But Vega says Yasiel says there must be some kind of mistake -- because he's certain he never touched her.
Puig was not arrested and no charges have been filed -- but MLB officials and the Dodgers have opened an investigation into the incident in hopes of figuring out what really went down.