[Thrain]

you cannot be in their direct field of vision and you have to make a succesful attack with in a round.

if you are a fighter/thief or fighter/mage/thief you may be using a weapon that you cannot backstab with. only weapons usable by the single class theif are allowed to backstab. basically, unless you're using a single handed bladed weapon (including the katana) or a club or a quarterstaff, you won't be able to backstab.