Can Resist Pain be cast on someone before they are injured?
No, as there is no pain to resist. Alternately, a gamemaster can allow it, but keep in mind that Resist Pain uses “Damage Value” as the basis for the Drain Value. This means that the caster needs to choose a Damage Value to apply the pain resistance for when casting the spell. If the subject suffers damage with a higher DV than Resist pain was cast for, it will have no effect.