You can only receive a short invincibility to run away from snipers in hall way and other maps, but you can shoot or throw grenades. And this may be removed 'arena' 'small maps' and other maps. This is just to make it harder for spawn campers to kill. If you don't like it find a server without it its only 3 seconds of invincibility.
Counter Argument: It does not matter 3-# seconds wont protect us from nothing. <<<Discuss that too