Rotating troops at the front of battle

[LorDBulA]

Do you press and hold alt while clicking behind your line?

Yes.

Does pressing alt make them backpeddle or something?

Normally if you order unit to move in the opposite direction it will rotate around center of formation ( assuming unit is aligned North to South soldier in the most south of the formation will march to the most north position ) and march to the spot and stop facing in the opposite direction then in the beginning.

With alt click all soldiers do about face. March to destination and do about face again. They end up facing the same direction as in the beginning.