One Piece Chapter 36, page 20: HUNTED!!

While bent backward, Luffy quickly uses his rubber legs to wrap around Kuro's neck and shoulders, pinning him. Kuro gasps in shock. Luffy shouts, "GOMU GOMU..." and slams his feet directly into Kuro's face with a loud impact (SFX: PLAK). Luffy then unleashes his attack, "SPEAR!!!!", driving Kuro face-first into the ground with immense force, kicking up a massive cloud of dust.