Doctor in fur causes fight (6)
I believe the answer is:
combat
'fight' is the definition.
(I know that fight can be written as combat)
'doctor in fur' is the wordplay.
'doctor' becomes 'MB' (Bachelor of Medicine, Medicinae Baccalaureus).
'in' indicates putting letters inside.
'fur' becomes 'coat' (an animal's coat).
'mb' going inside 'coat' is 'COMBAT'.
'causes' is the link.
(Other definitions for combat that I've seen before include "Battle, warfare" , "Fight, struggle or contest" , "War; contest" , "sort of jacket" , "Oppose" .)