Counterspelling is the act of a spellcaster countering any spells cast by an enemy spellcaster, which cancels out the spell being cast. Spellcraft is required to recognize the spell being cast, and then a suitable counterspell is required to be memorized by the Countering caster. Counterspelling was not implemented in NWN2 at the time of release. From the readme file p.104: Counterspelling is not possible in NWN2.