The flashbang is one of the 3 grenades available for humans featured in Counter-Strike: Source. The flashbang is an exception among the equipment as it cannot be used, along with the defusal kit and smoke grenade in Zombie Escape.
Most servers restrict the use of flashbangs. However, the GFLClan and Dreamevo servers, as well as the hellz.fr server in some while, made flashbangs available for all humans. They were not normal flashbangs, but they could be used to light up dark areas for a certain period.