Gold medallist takes head off part of the target (5)
I believe the answer is:
Here is my best explanation:
'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'.