In the poem "Barbara Frietchie" what happend before stonewall jackson yelled "Halt!"?

Up the street came the rebel tread,

Stonewall Jackson riding ahead.

Under his slouched hat left and right

He glanced: the old flag met his sight.

"Halt!" - the dust-brown ranks stood fast.

"Fire!" - out blazed the rifle-blast.

It shivered the window, pane and sash;

It rent the banner with seam and gash.