At this point Gen. George Meade completes a excellent maneurver placing the entire right wing of the union army on the confederate left and rear.

Gen. Lee was trapped. He had half of the Union Army in front and the other half blocking his rear. (This is called a pincher movement)

Hooker had Lee. But, he changed his orders and told Meade to pull back his men to the Chancellor House. (he switched from offensive to the defensive)

That gave the Confederates time to dig in and reinforce the left flank and rear.