Gold medallist takes head off part of the target (5)
I believe the answer is:
inner
'part of the target' is the definition.
'gold medallist takes head off' is the wordplay.
'gold medallist' becomes 'winner'.
'takes head off' means to remove the first letter (I've seen 'taking head off' mean this).
'winner' with its initial letter taken off is 'INNER'.
(Other definitions for inner that I've seen before include "Central area of a city, often old" , "Relating to the soul, mind or spirit" , "Annulus nearest bull" , "- - sanctum" , "Situated inside" .)