Roughly losing head in a fight (4)
I believe the answer is:
'a fight' is the definition.
'roughly losing head' is the wordplay.
'roughly' becomes 'about' (synonyms).
'losing head' means to remove the first letter.
'about' with its first letter removed is 'BOUT'.
'in' is the link.
(Other definitions for bout that I've seen before include "period in ring" , "Contest; illness episode" , "Period of activity or boxing contest" , "Wrestling contest" , "Wrestling/boxing match" .)