Attack fee (6)
I believe the answer is:
charge
I believe this clue is a double definition.
'attack' is the first definition.
(I know that attack can be written as charge)
'fee' is the second definition.
(I've seen this before)
(Other definitions for charge that I've seen before include "Load - price" , "Rush forward in attack" , "damage" , "Rush to exact payment?" , "Deliver an official injunction" .)