During the later period of the running battle around Lexington and Concord at the dawn of the American Revolution the British regulars under Lt Colonel Smith and Lord Percy who had respectively recently withdrawn from Concord and come to reinforce Smith were a pretty ragged bunch. Subjected to dis-concerting sniper fire for most of the day from colonial militia, Percy himself had had to stop his column several times to reform it back into proper marching order, hardly suited for the army which had won Europe from all comers in the Seven Years War.
Still, they had little else to fear. A now combined detachment some 1800 strong facing perhaps twice that in un-organized militia rabble, they could safely (in a somewhat stretched meaning of the word) proceed back to Boston at their leisure. The colonials simply didn't have the centralized leadership to accomplish such battlefield feats as encircling Lexington and moving in on the remaining regulars. They did indeed move back to Boston later in the day and, although they suffered casualties the whole way, they made it back a coherent and capable fighting force capable of continuing to occupy the city.
However, this presents an interesting possibility. What if a colonial militia commander had risen from simply trying to command his own company to trying to coordinate the efforts of the combined militia? Say one colonel Barret, who commanded the first tactical victory by the Patriot force at Concord a few hours earlier? Using Sons of Liberty couriers, say, he begins communicating with other company commanders to surround the town of Lexington and deny the red-coats their escape.
If he (and others) could keep the militia in one spot long enough (through the entire course of the day minutemen where arriving and leaving as their supply of powder and shot dictated), and they were to make an advance into the town, either annihilating the British force or coercing a surrender, what might this mean for the future of this theater (and the war in general)? The British force had already performed less than admirably when engaging colonials at Concord (light infantry from the Royal Marines, IIRC), botching their first volley and messing up the line transition and missing their opportunity at a second, and were apparently scared witless of the Americans after witnessing a militiaman 'scalping' a survivor of the bridge engagement (in reality finishing him with an ax), so it's not impossible for such a thing to happen, especially as the British force had spent the entire day being harried and harassed by irregulars and snipers, nary able to engage any but the occasional colonial group caught in the open.