You ward a creature within range against attack.
Until the spell ends, any creature who targets the warded creature with an attack or a harmful spell must first make a Wisdom saving throw. On a failed save, the creature must choose a new target or lose the attack or spell. This spell doesn’t protect the warded creature from area effects, such as the explosion of a fireball.
  If the warded creature makes an attack or casts a spell that affects an enemy creature, this spell ends.
  Wizard of the Coasts (2018): The final sentence now reads, “If the warded creature makes an attack, casts a spell that affects an enemy, or deals damage to another creature, this spell ends.”