Former "Bachelorette" star Kasey Kahl smashed a woman in the face at a Fresno nightclub, giving her a bloody nose ... this according to the alleged victim ... though Kasey claims it was all in self-defense.

TMZ broke the story ... Kahl was arrested early Sunday morning for drunk and disorderly conduct at Club Habano's nightclub.

According to the police report, obtained by TMZ, Kahl was accused of attacking a man named Richard Chaney outside the club ... and then smashing Chaney's girlfriend in the face when she tried to break up the fight.