Colonel Barrett's troops, upon seeing smoke rising from the village square as the British burned cannon carriages, and seeing only a few light infantry companies directly below them, decided to march back toward the town from their vantage point on Punkatasset Hill to a lower, closer flat hilltop about 300 yards (274 m) from the North Bridge.
As the militia advanced, the two British companies from the 4th and 10th Regiments that held the position near the road retreated to the bridge and yielded the hill to Barrett's men.

Five full companies of Minutemen and five more of militia from Acton, Concord, Bedford and Lincoln occupied this hill as more groups of men streamed in, totaling at least 400 against  Captain Laurie's light infantry companies, a force totaling 90–95 men.
Barrett ordered the Massachusetts men to form one long line two abreast on the highway leading down to the bridge, and then he called for another consultation.
While overlooking North Bridge from the top of the hill, Barrett, Lt.
Col.
John Robinson of Westford and the other Captains discussed possible courses of action.
 Captain Isaac Davis of Acton, whose troops had arrived late, declared his willingness to defend a town not their own by saying, "I'm not afraid to go, and I haven't a man that's afraid to go."

Barrett told the men to load their weapons but not to fire unless fired upon, and then ordered them to advance.
Laurie ordered the British companies guarding the bridge to retreat across it.
One officer then tried to pull up the loose planks of the bridge to impede the colonial advance, but Major Buttrick began to yell at the regulars to stop harming the bridge.
The Minutemen and militia from Concord, Acton and a handful of Westford Minutemen, advanced in column formation, two by two, led by Major Buttrick, Lt.
Col.
Robinson, then Capt.
Davis, on the light infantry, keeping to the road, since it was surrounded by the spring floodwaters of the Concord River.

Captain Laurie then made a poor tactical decision.
Since his summons for help had not produced any results, he ordered his men to form positions for "street firing" behind the bridge in a column running perpendicular to the river.
 This formation was appropriate for sending a large volume of fire into a narrow alley between the buildings of a city, but not for an open path behind a bridge.
Confusion reigned as regulars retreating over the bridge tried to form up in the street-firing position of the other troops.
Lieutenant Sutherland, who was in the rear of the formation, saw Laurie's mistake and ordered flankers to be sent out.
But as he was from a company different from the men under his command, only three soldiers obeyed him.
The remainder tried as best they could in the confusion to follow the orders of the superior officer.

A shot rang out.
It was likely a warning shot fired by a panicked, exhausted British soldier from the 43rd, according to Captain Laurie's report to his commander after the fight.
Two other regulars then fired immediately after that, shots splashing in the river, and then the narrow group up front, possibly thinking the order to fire had been given, fired a ragged volley before Laurie could stop them.

Two of the Acton Minutemen, Private Abner Hosmer and Captain Isaac Davis, who were at the head of the line marching to the bridge, were hit and killed instantly.
 Rev. Dr. Ripley recalled:
The Americans commenced their march in double file… In a minute or two, the Americans being in quick motion and within ten or fifteen rods of the bridge, a single gun was fired by a British soldier, which marked the way, passing under Col.
Robinson's arm and slightly wounding the side of Luther Blanchard, a fifer, in the Acton Company.

Four more men were wounded.
 Major Buttrick then yelled to the militia, "Fire, for God's sake, fellow soldiers, fire!"
At this point the lines were separated by the Concord River and the bridge, and were only 50 yards (46 m) apart.
 The few front rows of colonists, bound by the road and blocked from forming a line of fire, managed to fire over each other's
Colonel Barrett's troops, upon seeing smoke rising from the village square as the British burned cannon carriages, and seeing only a few light infantry companies directly below them, decided to march back toward the town from their vantage point on Punkatasset Hill to a lower, closer flat hilltop about 300 yards (274 m) from the North Bridge. As the militia advanced, the two British companies from the 4th and 10th Regiments that held the position near the road retreated to the bridge and yielded the hill to Barrett's men.
Five full companies of Minutemen and five more of militia from Acton, Concord, Bedford and Lincoln occupied this hill as more groups of men streamed in, totaling at least 400 against  Captain Laurie's light infantry companies, a force totaling 90–95 men. Barrett ordered the Massachusetts men to form one long line two abreast on the highway leading down to the bridge, and then he called for another consultation. While overlooking North Bridge from the top of the hill, Barrett, Lt. Col. John Robinson of Westford and the other Captains discussed possible courses of action.  Captain Isaac Davis of Acton, whose troops had arrived late, declared his willingness to defend a town not their own by saying, "I'm not afraid to go, and I haven't a man that's afraid to go."
Barrett told the men to load their weapons but not to fire unless fired upon, and then ordered them to advance. Laurie ordered the British companies guarding the bridge to retreat across it. One officer then tried to pull up the loose planks of the bridge to impede the colonial advance, but Major Buttrick began to yell at the regulars to stop harming the bridge. The Minutemen and militia from Concord, Acton and a handful of Westford Minutemen, advanced in column formation, two by two, led by Major Buttrick, Lt. Col. Robinson, then Capt. Davis, on the light infantry, keeping to the road, since it was surrounded by the spring floodwaters of the Concord River.
Captain Laurie then made a poor tactical decision. Since his summons for help had not produced any results, he ordered his men to form positions for "street firing" behind the bridge in a column running perpendicular to the river.  This formation was appropriate for sending a large volume of fire into a narrow alley between the buildings of a city, but not for an open path behind a bridge. Confusion reigned as regulars retreating over the bridge tried to form up in the street-firing position of the other troops. Lieutenant Sutherland, who was in the rear of the formation, saw Laurie's mistake and ordered flankers to be sent out. But as he was from a company different from the men under his command, only three soldiers obeyed him. The remainder tried as best they could in the confusion to follow the orders of the superior officer.
A shot rang out. It was likely a warning shot fired by a panicked, exhausted British soldier from the 43rd, according to Captain Laurie's report to his commander after the fight. Two other regulars then fired immediately after that, shots splashing in the river, and then the narrow group up front, possibly thinking the order to fire had been given, fired a ragged volley before Laurie could stop them.
Two of the Acton Minutemen, Private Abner Hosmer and Captain Isaac Davis, who were at the head of the line marching to the bridge, were hit and killed instantly.  Rev. Dr. Ripley recalled:
The Americans commenced their march in double file… In a minute or two, the Americans being in quick motion and within ten or fifteen rods of the bridge, a single gun was fired by a British soldier, which marked the way, passing under Col. Robinson's arm and slightly wounding the side of Luther Blanchard, a fifer, in the Acton Company.
Four more men were wounded.  Major Buttrick then yelled to the militia, "Fire, for God's sake, fellow soldiers, fire!" At this point the lines were separated by the Concord River and the bridge, and were only 50 yards (46 m) apart.  The few front rows of colonists, bound by the road and blocked from forming a line of fire, managed to fire over each other's
Battles of Lexington and Concord