Garment protecting doctor in fight (6)
I believe the answer is:
combat
'fight' is the definition.
(combat is a kind of fight)
'garment protecting doctor' is the wordplay.
'garment' becomes 'coat' (coating is a kind of garmenting**).
'protecting' means one lot of letters goes inside another.
'doctor' becomes 'mb' (Bachelor of Medicine, Medicinae Baccalaureus).
'coat' placed around 'mb' is 'COMBAT'.
'in' is the link.
(Other definitions for combat that I've seen before include "War; contest" , "Take action to deal with - fight" , "Oppose" , "Battle, warfare" , "Battle or fight" .)