CTV News
June 8, 2013

A man in an Afghan army uniform turned his weapon on American trainers working with him in the country's east on Saturday, killing three of them, while an attacker with a grenade killed an Italian soldier in the west, officials said.

(excerpted)
http://www.ctvnews.ca/world/man-in-afgha...0#ixzz2Vef6qWsP

Unfortunately,there is no way you can defend yourself against this. All you can do is kill them before they kill you if you survive the initial attack.

It's the major reason that Special Forces duty has always been so dangerous. You go in with a 12 man team and are immediately surrounded by hundreds of locals who you are arming and teaching them how to use the arms.