Sinclair, who was in an on-again, off-again relationship with Hugh Hefner's son since August 2010, said the couple had just moved in together when things went terribly wrong.
"We had just freshly moved into the apartment, and I know Marston was a little stressed out about it, and Marston has been unstable throughout the whole course of our relationship… and we got into an argument about something really silly and it kind of escalated and it became violent," Sinclair told E! News.
"Initially, he kicked me and I went backwards, I fell. Then he punched me and grabbed me up, and I scratched him to defend myself. It was very shocking."
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When cops showed up Marston denied Sinclair's allegations, but he was arrested anyway when she showed them her injuries. He has since been released on $200,000 bail.
The model also said she has yet to hear from anyone in the Playboy camp to make sure she's okay.
"Nobody, no support," the 20-year-old said. "Nobody's empathetic or concerned. It's more like, cover it up and protect the image, you know what I'm saying?"
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"In one aspect, I'm ridiculously offended by the way things are being handled, on the other aspect, I understand. It's family," she mused. "And they're looking out for their name, and I understand that, but they need to at least recognize what has happened and apologize for what has happened."
The only comment Hugh Hefner has made about the incident was to blow it off as a lovers' quarrel.
"If they care about each other, they'll patch it up," the Playboy founder told People.
Marston Hefner has not responded to requests for comment.