I first mentioned this idea on Google Plus as a spell shield. The idea is a defensive analogue to the recently posted maleficence rule.

Any prepared spell may be expended to protect one person per sorcerer level from the effects of one spell. A decision to use magical defense must be made before damage or saving throw dice are rolled. For example, a second level sorcerer may expend a prepared spell in order to protect two characters from some hostile magic.

This rule makes prepared spells function somewhat like magic hit points, as a potential buffer, and means that sorcerers can absorb a magical assault for a party in much the same way that warriors can serve as physical defenders. It also supports the classic wizard’s duel without requiring a separate mini-game.

The magical defense rules may be used with traditional levelled Vancian magic. In this case, the number of people that can be protected is equal to the level of the spell expended.