Abjuration [Force]
Level: Sorcerer 7, Wizard 7
Components: V, S
Casting Time: 1 swift action
Range: Personal
Target: You
Duration: 5 rounds
Spines of brilliant yellow light burst outward from your body, giving the impression that you are covered in glowing spikes.
You create a field of arcane force around your body that deals retaliatory damage to your attackers. While this spell is active, any creature striking you with a nonreach melee weapon takes 4d6 points of damage.
As part of the casting of this spell, if you are a sorcerer you can sacrifice one additional sorcerer spell slot of up to 9th level; this increases the damage dealt by 2 points for every level of the sacrificed slot. For example, if you use a 7th-level spell slot to cast justice of the wyrm king and sacrifice a 5th-level spell slot to augment it, you deal 4d6+10 points of damage to your attackers.
Source: Dragon Magic, page 69.