Although often styled a battle, in reality the engagement at Lexington was a minor brush or skirmish.
As the regulars' advance guard under Pitcairn entered Lexington at sunrise on April 19, 1775, about 80 Lexington militiamen emerged from Buckman Tavern and stood in ranks on the village common watching them, and between 40 and 100 spectators watched from along the side of the road.
 Their leader was Captain John Parker, a veteran of the French and Indian War, who was suffering from tuberculosis and was at times difficult to hear.
 Of the militiamen who lined up, nine had the surname Harrington, seven Munroe (including the company's orderly sergeant, William Munroe), four Parker, three Tidd, three Locke, and three Reed; fully one quarter of them were related to Captain Parker in some way.
 This group of militiamen was part of Lexington's "training band", a way of organizing local militias dating back to the Puritans, and not what was styled a minuteman company.

After having waited most of the night with no sign of any British troops (and wondering if Paul Revere's warning was true), at about 4:15 a.m., Parker got his confirmation.
 Thaddeus Bowman, the last scout that Parker had sent out, rode up at a gallop and told him that they were not only coming, but coming in force and they were close.
 Captain Parker was clearly aware that he was outmatched in the confrontation and was not prepared to sacrifice his men for no purpose.
 He knew that most of the colonists' powder and military supplies at Concord had already been hidden.
 No war had been declared. (
The Declaration of Independence was a year in the future.)
 He also knew the British had gone on such expeditions before in Massachusetts, found nothing, and marched back to Boston.

Parker had every reason to expect that to occur again.
The Regulars would march to Concord, find nothing, and return to Boston, tired but empty-handed.
He positioned his company carefully.
 He placed them in parade-ground formation, on Lexington Common.
 They were in plain sight (not hiding behind walls), but not blocking the road to Concord.
 They made a show of political and military determination, but no effort to prevent the march of the Regulars.
Many years later, one of the participants recalled Parker's words as being what is now engraved in stone at the site of the battle: "Stand your ground; don't fire unless fired upon, but if they mean to have a war, let it begin here."
According to Parker's sworn deposition taken after the battle:
I ... ordered our Militia to meet on the Common in said Lexington to consult what to do, and concluded not to be discovered, nor meddle or make with said Regular Troops (if they should approach) unless they should insult or molest us; and, upon their sudden Approach, I immediately ordered our Militia to disperse, and not to fire:—Immediately said Troops made their appearance and rushed furiously, fired upon, and killed eight of our Party without receiving any Provocation therefor from us.

— John Parker
Rather than turn left towards Concord, Marine Lieutenant Jesse Adair, at the head of the advance guard, decided on his own to protect the flank of the British column by first turning right and then leading the companies onto the Common itself, in a confused effort to surround and disarm the militia.
Major Pitcairn arrived from the rear of the advance force and led his three companies to the left and halted them.
The remaining companies under Colonel Smith lay further down the road toward Boston.
Although often styled a battle, in reality the engagement at Lexington was a minor brush or skirmish. As the regulars' advance guard under Pitcairn entered Lexington at sunrise on April 19, 1775, about 80 Lexington militiamen emerged from Buckman Tavern and stood in ranks on the village common watching them, and between 40 and 100 spectators watched from along the side of the road.  Their leader was Captain John Parker, a veteran of the French and Indian War, who was suffering from tuberculosis and was at times difficult to hear.  Of the militiamen who lined up, nine had the surname Harrington, seven Munroe (including the company's orderly sergeant, William Munroe), four Parker, three Tidd, three Locke, and three Reed; fully one quarter of them were related to Captain Parker in some way.  This group of militiamen was part of Lexington's "training band", a way of organizing local militias dating back to the Puritans, and not what was styled a minuteman company.
After having waited most of the night with no sign of any British troops (and wondering if Paul Revere's warning was true), at about 4:15 a.m., Parker got his confirmation.  Thaddeus Bowman, the last scout that Parker had sent out, rode up at a gallop and told him that they were not only coming, but coming in force and they were close.  Captain Parker was clearly aware that he was outmatched in the confrontation and was not prepared to sacrifice his men for no purpose.  He knew that most of the colonists' powder and military supplies at Concord had already been hidden.  No war had been declared. (The Declaration of Independence was a year in the future.)  He also knew the British had gone on such expeditions before in Massachusetts, found nothing, and marched back to Boston.
Parker had every reason to expect that to occur again. The Regulars would march to Concord, find nothing, and return to Boston, tired but empty-handed. He positioned his company carefully.  He placed them in parade-ground formation, on Lexington Common.  They were in plain sight (not hiding behind walls), but not blocking the road to Concord.  They made a show of political and military determination, but no effort to prevent the march of the Regulars. Many years later, one of the participants recalled Parker's words as being what is now engraved in stone at the site of the battle: "Stand your ground; don't fire unless fired upon, but if they mean to have a war, let it begin here." According to Parker's sworn deposition taken after the battle:
I ... ordered our Militia to meet on the Common in said Lexington to consult what to do, and concluded not to be discovered, nor meddle or make with said Regular Troops (if they should approach) unless they should insult or molest us; and, upon their sudden Approach, I immediately ordered our Militia to disperse, and not to fire:—Immediately said Troops made their appearance and rushed furiously, fired upon, and killed eight of our Party without receiving any Provocation therefor from us.
— John Parker
Rather than turn left towards Concord, Marine Lieutenant Jesse Adair, at the head of the advance guard, decided on his own to protect the flank of the British column by first turning right and then leading the companies onto the Common itself, in a confused effort to surround and disarm the militia. Major Pitcairn arrived from the rear of the advance force and led his three companies to the left and halted them. The remaining companies under Colonel Smith lay further down the road toward Boston.
Battles of Lexington and Concord