Attack right back in box that's well defended (6)
I believe the answer is:
strafe
'attack right back' is the definition.
'strafe' can be an answer for 'attack' (to strafe is to attack from the air). I'm not sure about the 'right back' bit.
'in box that's well defended' is the wordplay.
'in' is an insertion indicator.
'box' becomes 'safe' (safe is a kind of box).
'that's well defended' becomes 'tr' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'safe' going around 'tr' is 'STRAFE'.
Can you help me to learn more?
(Other definitions for strafe that I've seen before include "bombing raid" , "Spray with gunfire" , "Make 'Raking Fire'" , "Fire from the air with machine guns" , "Spray with bullets" .)