Become twisted fighting police initially (4)
I believe the answer is:
warp
'become twisted' is the definition.
(I've seen this before)
'fighting police initially' is the wordplay.
'fighting' becomes 'war'.
'initially' says to take the initial letters.
The first letter of 'police' is 'p'.
'war'+'p'='WARP'
(Other definitions for warp that I've seen before include "Of wood, twist under heat" , "Distort, twist" , "Go out of shape" , "Distort, ship's rope" , "Abnormality in character" .)