Hammer thrower nicked the gold (4)
I believe the answer is:
thor
'hammer thrower' is the definition.
(the Norse god Thor wields a hammer)
'nicked the gold' is the wordplay.
'nicked' becomes 'th' (I am not sure about this - if you are sure you should believe this answer much more).
'the gold' becomes 'or' ('or' is the heraldic name for gold).
'th'+'or'='THOR'
Can you help me to learn more?
(Other definitions for thor that I've seen before include "Wielder of hammer" , "Norse god of thunder - a weekday is named after him" , "One of the Norse gods" , "Divine figure" , "Mythical figure" .)