After the British were repelled at North Bridge, they decided to leave Concord and march back to Boston. The American militiamen initially stood silently and watched the departure, but later the local men began to take positions behind trees and fences and pour fire into the departing army. The church bells continued their tolling and increasing numbers of farmers and workmen left their tasks to join the rout.
The British were outraged by the American tactics, believing that real soldiers would confront their enemies in the open. Instead, the colonists would open fire from hidden positions as the army passed, then sprint ahead to another protected spot and repeat the process. The tired and angry British soldiers broke into houses along the path of retreat; any man remotely suspected of being one of the snipers was shot and his house burned.
British prospects improved somewhat in Lexington where they finally linked up with the relief forces. Two cannon had been brought from Boston and were used with some effect on the march back. Nevertheless, sniper attacks dogged the British to the city outskirts. At the end of the day, American militiamen began to encircle Boston and started the siege of Boston. And the American Revolution has begun.
The British listed their casualties for the Concord and the retreat to Boston as over 70 killed and around 150 wounded.