Brazilian star Polyana Viana was waiting for an Uber in Jacarepagua, Rio de Janeiro, when the thief ordered her to hand over her phone, warning that he was armed.
But the 26-year-old lashed out, kicking and punching him before putting him in a martial arts chokehold while she waited for police to arrive.
UFC president Dana White shared a photo of the man's gruesome facial injuries after his beating. Another shows the 'weapon' was actually just a cardboard cut-out.
She told MMA Junkie how the man asked her for the time and then saw he was not going to leave.
'So I already moved to put my cell phone in my waist. And then he said, "Give me the phone. Don’t try to react, because I’m armed".
'Then he put his hand over [a gun], but I realised it was too soft.'
'He was really close to me. So I thought, "If it’s a gun, he won’t have time to draw it". So I stood up I threw two punches and a kick.
'He fell, then I caught him in a rear-naked choke. Then I sat him down in the same place we were before and said, "Now we’ll wait for the police"'. Girl like VIANA!