Manipulating arcane power is a dangerous task requiring focus and concentration.
When an arcane caster manipulates the raw energies of reality, it can overwhelm them causing a backlash as reality snaps back into shape. This creates a wave of destructive energies beginning at the caster and radiating out to a distance based on how powerful the failed spell was intended to be.
Damage is 1d6 per level of the failed spell. The Caster cannot save against this damage regardless of safeguards or items in their possession. They are actively manipulating the energy thus forgoing any innate protection.
The range of the effect is a base five feet increasing by five feet per spell level centered on the Caster.
An arcane caster can purposefully fail a concentration check. This is known an Arcane Retribution. It is because of this behavior during wars between various rivals throughout history that arcane casters are shunned. The collateral damage caused from this type of action can be significant.