Question

Why is fighting on the defensive such an advantage for untrained troops?

Answer 1

Because they don't have to go into enemy lines, which requires mental training and physical, as well. They just see the invading troops, and attack, rather than planning and attacking.

Answer 2

When being defensive, untrained troops do not export as much energy, effort, and power as they would have if they were offensive (attack). It also gives them a perspective of the enemy's tactics and warfare charge.