'Orange is the New Black' Star Ruby Rose -- Girl-On-Girl Beatdown (Video)

Before "Orange Is The New Black" star Ruby Rose was everyone's girl crush ... she was crushing heads ... and TMZ Sports has video of her busting faces in an amateur boxing match back in Australia.

Ruby -- a huge VJ down under before becoming America's Netflix obsession -- stepped into the squared circle in October 2012 and swapped lady leather with a woman named Yi Sia.

Rose DOMINATED the fight from start to finish ... beating Sia so badly, that she turned her back to Ruby during one particularly brutal combination ... just so she could avoid further punishment.

Makes sense ... since Rose claims to have been boxing FULL TIME at one point in her life, and happens to be the the god-daughter of former WBA World Bantamweight Champion Lionel Rose.

No wonder the chicks at Litchfield Penitentiary don't want any beef ...