What explains the high number of casualties the british suffered in their campaign against concord?

The high casualties incurred by the British army at Concord can be attributed to the use of guerrilla tactics by colonial militiamen. Instead of coming out to face the British head-on in the traditional massed battles for which the British had trained and schemed, the colonial militias used hit-and-run tactics along the way to Concord, striking quickly, inflicting casualties, and disappearing before the formed British troops could react.

Do you have more info about it ? i doubt this is the answer because i don't have all the information but if trouble was brewing in a clinic maybe it was an argument as to which clinic was better or smth of that nature