A female MMA fighter put the SMACK down on an alleged male attacker who tried to rob her in Brazil last night ... choking the guy into submission with her legs ... and it was caught on video.

The bad ass crime stopper is Monique Bastos -- who says she was on her way to jiu-jitsu training when she was attacked by two men who demanded her cell phone.

Monique told MMAFighting.com one of the men was able to run off with the cell -- but she managed to trip up the second guy ... and locked him up in a triangle choke.

The video is insane ... you can see the alleged attacker BEGGING for mercy. She held the guy for 15 minutes before cops came and arrested the suspect.

Unfortunately, Bastos says the situation was all too familiar ... as she had been robbed in the past.

"I’ve been through this a few times before, and it’s the second time I fought back."