Battle of Groveton Aug 1862

[2-81 Armor]

Manassas, Second  

Other Names: Manassas, Second Bull Run, Manassas Plains, Groveton, Gainesville, Brawner's Farm

https://www.nps.gov/abpp/battles/va026.htm

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It is one of the many names given to the battle of Second Manassas.

I see. Thanks for the explanation.
It seems then the union troops were marching to join Popes army when confederate troops
moving into position to attack Pope bumped into them?

That's mostly correct. Basically Jackson had taken up his (almost) final position on the battlefield near the railroad cut after taking the Manassas Depot, and was wanting to draw Pope's attention to his presence so Longstreet could arrive unmolested. Pope being Pope, Jackson went undiscovered, and so he initiated the action at Brawner's in order to more or less force the issue.