However as with most things Palin it's mostly bullshit.
This according to Snopes:
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, and in October 2011 he was sentenced to life in prison. (Attaway faced the maximum sentence on all assault and theft charges because he was a convicted felon with 30 prior arrests on his record.)
However, what makes this incident an enduring item of interest on the Internet is an account of the crime which was circulated via e-mail in December 2010 (reproduced as the first item in the Examples section above) and presented as a 27 November Associated Press account of the incident. While that account was indeed based on an Associated Press news article, it contained a paragraph not found in the original:
"The suspect was transported to the local hospital with two broken arms, a broken leg, possible broken ribs, assorted lacerations and bruises he obtained when he fell trying to run after stabbing the Marine."
(The audience is supposed to read between the lines in the preceding text and conclude that the suspect did not fall but rather was beaten by the other three Marines.)
None of the news accounts, police reports, or interviews about this incident indicated that Attaway was injured, either while being subdued or afterwards. That bit was pure invention on the part of some person who inserted the additional paragraph into the news account, thereby transforming it into a "Don't mess with the Marines" object lesson.
So not only is this story at least five years old, but the part that was supposed to impress about our military is a complete fabrication.
Kind of like Palin herself.