The clash between the two gangs took place ten years before the actual plot of One Piece began, when Luffy was still a child. Shanks and his pirates were hanging out at Makino’s bar when Grizzly entered with his bandits. The bandit leader tried to provoke Shanks by smashing the offered bottle along with several others. However, Shanks remained calm. Luffy, who was getting on his nerves, yelled at Shanks why he didn’t fight back. But the latter only said that a broken bottle was no cause for excitement.
Later, when Luffy took on the raiders to defend the pirates, he was attacked by Grizzly and dragged out of the bar. He tried to kill the boy and didn’t respond to the mayor’s appeasements either. But suddenly Shanks’ gang showed up.
The latter said that he could laugh about many things, be it a broken bottle or a destroyed bar, but he would not forgive anyone who dared to harm a friend. When one of the robbers then drew his gun and held it to the pirate captain’s head, Shanks remained calm and only warned him that his life was at stake. The latter looked incredulous, but was shot by Lucky Roux the next moment.
The rest of the mountain bandits wanted to avenge their dead comrade and attacked Shanks with drawn swords. But again he showed no emotion. His vice-captain, Benn Beckman, stepped forward and took on all comers. To do so, he simply struck at them with his rifle, taking them out with ease. Grizzly got scared and tried to negotiate with Shanks, but he didn’t go for it. The leader of the robbers now threw a smoke bomb on the ground and made off with Luffy.