Final answer:
John Adams grabbed his weapon or firefighting equipment when he heard the cry of "fire." He defended the soldiers involved in the Boston Massacre and believed they had the right to be represented in court.
Step-by-step explanation:
When John Adams heard the cry of "fire," he grabbed his weapon or his firefighting equipment, depending on the context. In the given historical context of the Boston Massacre, John Adams defended the soldiers involved in the incident. He grabbed the opportunity to represent the soldiers in court, believing they had the right to a fair trial. By doing so, John Adams may have also wanted to avoid any embarrassing questions about who first yelled "fire."