Ah, this one's been around a block a few times on the internet, it's partially true but someone did some embellishment, there's another version with British SAS instead of the USMC.
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On 26 November 2010 (Black Friday) at about 1:15 p.m., those manning the surveillance cameras at a Best Buy in Augusta, Georgia, spotted a shopper cutting a Dell laptop computer from its packaging and stuffing it down his pants. According to police, store security personnel approached the suspect, 39-year-old Tracey Attaway of Waynesboro, Georgia, and asked him to return the merchandise. Attaway became angry, released the laptop, and ran out the front door, pulling a knife and knocking down a Best Buy employee in the process.
Outside the store's entrance were four Marines and seven volunteers collecting donations for Toys for Tots. One of them, Cpl. Phillip Duggan, clotheslined the running man, bringing him to the ground. The assailant regained his feet and swung his knife, stabbing Duggan, then was quickly tackled by several other Marines and members of the store's loss-prevention team, who held him in the parking lot until deputies arrived.
The injured Marine was taken to Eisenhower Army Medical Center and released after receiving stitches. He was well enough the next day to drop off a toy for donation at a nearby Walmart.
Cpl. Duggan's attacker, Tracey Attaway, was jailed and charged with armed robbery, aggravated assault and possession of a knife in the commission of a crime. He was denied bond on 11 December 2010.