Swapping knight for rook, alter attack (6)
I believe the answer is:
charge
'attack' is the definition.
(I know this)
'swapping knight for rook alter' is the wordplay.
I cannot quite understand how this works, but
'rook' could be 'r' (chess abbreviation) and 'r' is located in the answer.
'alter' could be 'age' (ageing is a kind of altering) and 'age' is found in the leftover letters.
The remaining letters 'ch' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for charge that I've seen before include "protection" , "Rush forward in attack" , "Legal accusation" , "Deliver an official injunction" , "Offensive - fee" .)