Fighting opening of prong in buckle (4)
I believe the answer is:
warp
'buckle' is the definition.
(I know that buckle can be written as warp)
'fighting opening of prong' is the wordplay.
'fighting' becomes 'war'.
'opening of' says to take the initial letters.
The initial letter of 'prong' is 'p'.
'war'+'p'='WARP'
'in' is the link.
(Other definitions for warp that I've seen before include "Misintepret" , "'Bend out of shape, with heat say (4)'" , "Buckle" , "Go out of shape" , "Abnormality in character" .)