Can someone help me with infromation about the below-listed skirmish fought in the vicinity Hanover, New Jersey?

My ancestor Sergeant Colin McLachlan was in Hazen's Regiment (AKA "Congress's Own"). I found his military pension file in the National Archives and he wrote, "I was in several skirmishes and engagements, such as surprising the enemy at Hanover in 1777 where severals of them were either killed or wounded, by only two small companies under the command of Captains Heron and Chambers, without the loss of any on our side." I have checked many sources and none mention this skirmish. But I did narrow down the time-frame of the skirmish to July 26 – August 21, 1777 when the regiment (under Sullivan's Division) was camped at Hanover. On or about August 21, 1777 the Regiment left their encampment at "Bottle Hill" (today Madison, NJ).

Anyone with information please help!