Doctor in cape, fighting (6)
I believe the answer is:
combat
'fighting' is the definition.
('combat' can be a synonym of 'fighting')
'doctor in cape' is the wordplay.
'doctor' becomes 'mb' (Bachelor of Medicine, Medicinae Baccalaureus).
'in' is an insertion indicator.
'cape' becomes 'coat' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'mb' inserted inside 'coat' is 'COMBAT'.
Can you help me to learn more?
(Other definitions for combat that I've seen before include "Oppose" , "Fight or contest, may be mortal" , "War; contest" , "Battle or fight" , "Fight against; fighting" .)