Which is better for power to have the right foot underneath the right arm pit or behind the right arm pit?
Your legs act as posts to create a structure. Allow someone to push you (even slowly) with your feet under you and you'll very quickly find yourself falling backwards (or forwards if you try it from behind, though that's highly unlikely in boxing). Spread your feet, repeat and you'll immediately feel the increase in stability. Imagine you are moving your head defensively, your head must never move past your foot. If that has happened then you don't have a post under you, your structure in compromised and thus you have no balance. Watch boxers who do pull counters, if their head is pulled back further than their rear foot then they are off balance. If their head does not go past their foot then they have the balance to get back into position or transition into another technique i.e. punch or head movement.
