Hammerfist (3.5e Martial Artist Maneuver)
From D&D Wiki
Strike your opponents as hard as though you are using hammer leaving them stunned and vulnerable to additional attacks.
Level: Hard 5
Prerequisite: Four Hard flow maneuvers.
Description: A simple technique that use the bottom of the fist to attack the opponent. This maneuver does 8d8 plus 1.5x str mod point of damage. An opponent hit by this maneuver must make a fortitude save with a d of 15 + 1/2 initiator level + str mod or be stunned for 1d4+2 rounds.
Special: This maneuver can be initiated using both hands doing 12d8 + twice str mod. Opponent must make a fort save of 20 + 1/2 initiator level + twice str mod or be stunned for 2d4+4 rounds.