The USS Chesapeake and HMS Leopard Affair.
On June 22, 1807, the United States frigate Chesapeake cleared Norfolk area waters for the Mediterranean to relieve the USS Constitution as flagship of the European station. In command was Captain (later Commodore) James Barron, who had been the senior officer aboard for only one day. [Source]
The HMS Leopard pursued, attacked and boarded the USS Chesapeake looking for deserters from the British Navy. [Source]
The Chesapeake/Leopard incident can be considered one of the causes of the conflict.