One Piece Chapter 6, page 21: Chapter 6: Number One

Luffy's Gum-Gum Pistol punch connects perfectly with Helmeppo's face, sending him flying with a loud "WAKH!" and "OOF!!!" sound effect. Luffy smiles and says, "NICE..." as Helmeppo is knocked out cold. Meanwhile, behind Luffy, Captain Morgan is suddenly frozen mid-swing, his massive axe-hand stopped in its tracks.