"When he started reaching into his pants like he had a weapon that's when I did something just to protect my girlfriend," West told WFLA.
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West, who is a trained fighter, wrestled with Nemeth. The two knocked over merchandise and West ripped Nemeth's sweatshirt off. Nemeth was knocked unconscious by West who subdued him before police arrived.
Nemeth was taken to the hospital for treatment, then to Manatee County Jail.
Nemeth, who did not have a gun, was arrested and charged with armed robbery.
Police did not encourage West's behavior, but appreciated him helping out, according to WFLA.
"He had some pretty good right crosses on him, Bradenton police Lt. James Racky told WFLA.