two things surprised the British:
American Forces along the beach on the left flank repulsed the British flanking forces consisting elite Light Infantry. If these hadn’t been rejected, the British would have attacked the central American Forces in the side, and rear
others said, the American Forces withstood two frontal assaults and didn’t succumb until out of ammunition, inflicting heavy casualties.Even after the flanking attack failed, British leadership did not think the American Forces would stand up to a determined frontal assault. In the Battle of Lexington and Concord, American militias were good at harassment fire of the British column but repeatedly broke when faced with close quarter fighting. This was why the British column made it back to Boston and wasn’t destroyed in the fighting retreat (the Continental Army of two years later would have wiped out the British Force). The British leadership thought this would happen again. The militias would fire a few ragged volleys and then break. But they did not. After this, the British fought much more cautiously, such as the Battles around NYC in 1776, where they used maneuver to defeat American forces and capture the city instead of just frontal attacks.
