Knockback Strike

 
Prerequisite(s): Wis 13+, Improved Unarmed Attack, Stunning Fist or Stunning Attack ability
 
Benefit: By giving up one of your stunning attacks for the day, you can imbue an unarmed strike with enough energy to cause an opponent to fly backwards through the air. In addition to taking normal damage from your attack, unless your opponent makes a Fortitude saving throw, (DC equal to 10 + half your level + your Wisdom bonus) a Knockback Strike causes them to be knocked directly away 10 feet and become prone, as if tripped. Hitting a wall, a large object, or another character does not cause additional damage, but does stop movement into that square. This ability can only be used once per round. This feat does not work on creatures more than two size categories larger than you.
 
Source: Races of Stone, Beyond Monks