Twist chimp's tail after fighting (4)
I believe the answer is:
warp
'twist' is the definition.
(I've seen this before)
'chimp's tail after fighting' is the wordplay.
'tail' indicates one should take the final letters.
'after' means one lot of letters go next to another.
'fighting' becomes 'war'.
The last letter of 'chimp' is 'p'.
'p' after 'war' is 'WARP'.
(Other definitions for warp that I've seen before include "Pervert - lengthways threads" , "Abnormality in character" , "Twist out of shape" , "Misintepret" , "Crane fly larva" .)