Difference in body having struck head (4)
I believe the answer is:
tiff
'difference' is the definition.
(I know that tiff is a type of dustup)
'body having struck head' is the wordplay.
'body' becomes 'stiff' (stiff is a kind of body).
'having struck head' means to remove the first letter.
'stiff' with its first letter taken away is 'TIFF'.
'in' is the link.
(Other definitions for tiff that I've seen before include "dispute" , "Lovers' row" , "A small quarrel or spat" , "Slight quarrel" , "causing quarrel" .)