Shamrock -- whose nickname is "The World's Most Dangerous Man" -- was hangin' out at a mall in Modesto, CA last month when he saw two women fighting each other in front of the Coach store ... surrounded by a group of lookie loos filming the whole thing.
We're told Shamrock dove into the scrap and tried to pry the women apart ... when one of the bystanders, a HEAVYSET bystander, jumped on his back and tried to rip Ken out of the pile.
Shamrock's rep tells TMZ ... he threw the person off of his back and followed up with a move that knocked the attacker to the ground.
After the person was incapacitated, the crowd shouted at Ken, "You just hit a girl." Ken took a closer look and realized the attacker was in fact a female .. so he immediately backed off.
An officer arrived to the scene and took a battery report against Shamrock, noting the only injury was a slight abrasion to the woman's knee. The report was sent to the District Attorney's Office.
But law enforcement sources tell TMZ ... Shamrock probably won't be prosecuted because officials don't feel the woman he knocked to the ground is a "victim." In fact, they believe Ken was acting in self-defense.
Shamrock's rep notes, "Outside the ring, Ken is not a violent man ... and was only trying to do the right thing."