The Ultimate Fighting Championship hall of fame member -- dubbed "The World's Most Dangerous Man" by ABC News early in his career -- was in a Modesto, Calif., mall last month when he saw two women fighting in front of a Coach Inc. luxury leather goods store, TMZ reported.
When Shamrock tried to separate the women, a "heavyset" bystander jumped on his back and tried to pull Shamrock out of the pile, the Web site said.
Shamrock, 48, threw the person off his back "and followed up with a move that knocked the attacker to the ground," a Shamrock representative told the site.
After the person was incapacitated, the crowd shouted, "You just hit a girl," the Web site reported.
Shamrock then realized the attacker was a woman "so he immediately backed off," the site said.
An officer took a battery report against Shamrock and sent it to the Stanislaus County District Attorney's Office, noting the only injury was a slight abrasion to the woman's knee, the site said.
The district attorney's office had no immediate comment.
An employee of the Coach store in Modesto's Vintage Faire Mall told United Press International Friday she couldn't comment on the incident.
Law enforcement sources told TMZ Shamrock would probably not be prosecuted because officials don't consider the woman he knocked to the ground a "victim."
They said they believed Shamrock was acting in self-defense.
"Outside the ring, Ken is not a violent man ... and was only trying to do the right thing," the Shamrock representative told the site.