One Piece Chapter 6, page 20-21: Chapter 6: Number One

Koby suddenly spots danger and screams, "LUFFY!! BEHIND YOU!" Helmeppo panics, shouting, "HEY! I TOLD YOU NOT TO MOVE OR I'D SHOOT! FINE! I'LL JUST SHOOT HIM THEN!" Luffy ignores Helmeppo's threat and winds up his arm, preparing his signature attack: "GUM-GUM..." Behind Luffy, Captain Morgan slowly rises, raising his giant axe-hand to strike, roaring, "YOU'VE ASSAULTED AN OFFICER OF THE NAVY!!!" Seeing this, Zoro calmly prepares to draw his sword with a quiet "KLMP" sound effect. Luffy launches his punch at Helmeppo, shouting, "...PISTOL!" while Helmeppo desperately screams, "DADDY!! KILL HIM!!

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.