A British officer (probably Pitcairn, but accounts are uncertain, as it may also have been Lieutenant William Sutherland) then rode forward, waving his sword, and called out for the assembled militia to disperse, and may also have ordered them to "lay down your arms, you damned rebels!"
Captain Parker told his men instead to disperse and go home, but, because of the confusion, the yelling all around, and due to the raspiness of Parker's tubercular voice, some did not hear him, some left very slowly, and none laid down their arms.
Both Parker and Pitcairn ordered their men to hold fire, but a shot was fired from an unknown source.

[A]t 5 o'clock we arrived [in Lexington], and saw a number of people, I believe between 200 and 300, formed in a common in the middle of town; we still continued advancing, keeping prepared against an attack though without intending to attack them; but on our coming near them they fired on us two shots, upon which our men without any orders, rushed upon them, fired and put them to flight; several of them were killed, we could not tell how many, because they were behind walls and into the woods.
We had a man of the 10th light Infantry wounded, nobody else was hurt.
We then formed on the Common, but with some difficulty, the men were so wild they could hear no orders; we waited a considerable time there, and at length proceeded our way to Concord.

— Lieutenant John Barker, 4th Regiment of Foot
According to one member of Parker's militia, none of the Americans had discharged their muskets as they faced the oncoming British troops.
The British did suffer one casualty, a slight wound, the particulars of which were corroborated by a deposition made by Corporal John Munroe.
Munroe stated that:
After the first fire of the regulars, I thought, and so stated to Ebenezer Munroe ...who stood next to me on the left, that they had fired nothing but powder; but on the second firing, Munroe stated they had fired something more than powder, for he had received a wound in his arm; and now, said he, to use his own words, 'I'll give them the guts of my gun.'
We then both took aim at the main body of British troops the smoke preventing our seeing anything but the heads of some of their horses and discharged our pieces.

Some witnesses among the regulars reported the first shot was fired by a colonial onlooker from behind a hedge or around the corner of a tavern.
Some observers reported a mounted British officer firing first.
Both sides generally agreed that the initial shot did not come from the men on the ground immediately facing each other.
Speculation arose later in Lexington that a man named Solomon Brown fired the first shot from inside the tavern or from behind a wall, but this has been discredited.
 Some witnesses (on each side) claimed that someone on the other side fired first;  however, many more witnesses claimed to not know.
 Yet another theory is that the first shot was one fired by the British, that killed Asahel Porter, their prisoner who was running away (he had been told to walk away and he would be let go, though he panicked and began to run).
 Historian David Hackett Fischer has proposed that there may actually have been multiple near-simultaneous shots.
 Historian Mark Urban claims the British surged forward with bayonets ready in an undisciplined way, provoking a few scattered shots from the militia.
 In response the British troops, without orders, fired a devastating volley.
 This lack of discipline among the British troops had a key role in the escalation of violence.

Witnesses at the scene described several intermittent shots fired from both sides before the lines of regulars began to fire volleys without receiving orders to do so.
A few of the militiamen believed at first that the regulars were only firing powder with no ball, but when they realized the truth, few if any of the militia managed to load and return fire.
The rest ran for their lives.

We Nathaniel Mulliken, Philip Russell, [and 32 other men ...] do testify and declare, that on the nineteenth in the morning, being informed that .
A British officer (probably Pitcairn, but accounts are uncertain, as it may also have been Lieutenant William Sutherland) then rode forward, waving his sword, and called out for the assembled militia to disperse, and may also have ordered them to "lay down your arms, you damned rebels!" Captain Parker told his men instead to disperse and go home, but, because of the confusion, the yelling all around, and due to the raspiness of Parker's tubercular voice, some did not hear him, some left very slowly, and none laid down their arms. Both Parker and Pitcairn ordered their men to hold fire, but a shot was fired from an unknown source.
[A]t 5 o'clock we arrived [in Lexington], and saw a number of people, I believe between 200 and 300, formed in a common in the middle of town; we still continued advancing, keeping prepared against an attack though without intending to attack them; but on our coming near them they fired on us two shots, upon which our men without any orders, rushed upon them, fired and put them to flight; several of them were killed, we could not tell how many, because they were behind walls and into the woods. We had a man of the 10th light Infantry wounded, nobody else was hurt. We then formed on the Common, but with some difficulty, the men were so wild they could hear no orders; we waited a considerable time there, and at length proceeded our way to Concord.
— Lieutenant John Barker, 4th Regiment of Foot
According to one member of Parker's militia, none of the Americans had discharged their muskets as they faced the oncoming British troops. The British did suffer one casualty, a slight wound, the particulars of which were corroborated by a deposition made by Corporal John Munroe. Munroe stated that:
After the first fire of the regulars, I thought, and so stated to Ebenezer Munroe ...who stood next to me on the left, that they had fired nothing but powder; but on the second firing, Munroe stated they had fired something more than powder, for he had received a wound in his arm; and now, said he, to use his own words, 'I'll give them the guts of my gun.' We then both took aim at the main body of British troops the smoke preventing our seeing anything but the heads of some of their horses and discharged our pieces.
Some witnesses among the regulars reported the first shot was fired by a colonial onlooker from behind a hedge or around the corner of a tavern. Some observers reported a mounted British officer firing first. Both sides generally agreed that the initial shot did not come from the men on the ground immediately facing each other. Speculation arose later in Lexington that a man named Solomon Brown fired the first shot from inside the tavern or from behind a wall, but this has been discredited.  Some witnesses (on each side) claimed that someone on the other side fired first;  however, many more witnesses claimed to not know.  Yet another theory is that the first shot was one fired by the British, that killed Asahel Porter, their prisoner who was running away (he had been told to walk away and he would be let go, though he panicked and began to run).  Historian David Hackett Fischer has proposed that there may actually have been multiple near-simultaneous shots.  Historian Mark Urban claims the British surged forward with bayonets ready in an undisciplined way, provoking a few scattered shots from the militia.  In response the British troops, without orders, fired a devastating volley.  This lack of discipline among the British troops had a key role in the escalation of violence.
Witnesses at the scene described several intermittent shots fired from both sides before the lines of regulars began to fire volleys without receiving orders to do so. A few of the militiamen believed at first that the regulars were only firing powder with no ball, but when they realized the truth, few if any of the militia managed to load and return fire. The rest ran for their lives.
We Nathaniel Mulliken, Philip Russell, [and 32 other men ...] do testify and declare, that on the nineteenth in the morning, being informed that .
Battles of Lexington and Concord