Knockback

Knockback (Weapon Property)

Price: +1 bonus
Property: Weapon
Caster Level: 11th
Aura: Moderate; (DC 20) evocation
Activation: Swift (command)
This weapon looks broader and thicker than a typical item of its type. A ram’s head with curling horns decorates its head or hilt.
Three times per day, you can activate this weapon and use it to drive your opponent back. The next time you hit a creature with the weapon before the end of your turn, the target must succeed on a DC 19 Fortitude save or be pushed back 5 feet.
If the target can’t move back, this ability has no effect. The knockback property works only on creatures of your own size category or smaller.
Prerequisites: Craft Magic Arms and Armor, repulsion.
Cost to Create: Varies.

Source: Magic Item Compendium