This spell summons a magical cage that appears foot behind you and your target creating a 20ft by 20ft barrier which nobody can enter or exit. If anyone tries to leave or enter the cage they are dealt 4d10 continuous damage per minute until they retreat. This means good or bad you and your opponent are locked in the cage together for 5 rounds. If anyone inside or outside attacks the barrier they will take any damage they attempted to deal to the target on the other side of the barrier.

Prerequisite; your opponent must be within 18ft of you to cast the spell or you will be locking yourself in the cage alone. You may also use this spell to cast it around yourself and your allies as a protective barrier. 

Teleportation spells are useable in the cage and give you the ability to escape the cage without consequences. It's up to the DM to decide if spells cast on people inside the cage affect the caster (if the spell must pass through the cage to reach the target then the spell does affect the caster. e.g. if the spell shoots a fireball at the target the cage blocks the spell and deals the above damage to the caster. If the spell sets fire to the ground under a targets feet the DM decides if the cage will block it.)