27-year-old Huerta -- who was once featured on the cover of Sports Illustrated -- was in front of a bar in Austin around 2 AM on Saturday morning ... when some other people began fighting. Roger was near the scuffle ... when he saw one of the men involved punch a female who was standing near the ruckus.
Once Huerta sees the woman collapse to the ground -- he instantly tries to confront the attacker saying, "You just punched a f**kin' girl."
Moments later, Huerta takes off his shirt ... slams his hat to the ground ... and rushes after the man.
Chaos ensues and people scramble after the fighters, blocking the camera -- but seconds later ... a shirtless Huerta can be seen finishing his attack on the other man ... who is sprawled out on the street.
People rush in to aid the bloody man on the ground -- who eventually gets off the pavement -- as Huerta walks away from the battle ground.
Austin PD tells TMZ that officers were called to the scene -- but so far, no arrests have been made.
Huerta's manager tells us, "I have not spoken to Roger yet about this incident, but I can say that it's in his nature to be very protective of women."