Cast takes on a hunt (6)
I believe the answer is:
forage
'hunt' is the definition.
(forage is a kind of hunt)
'cast takes on a' is the wordplay.
'cast' becomes 'forge' (as in casting or forging from metal).
'takes on' means one lot of letters goes inside another.
'forge' placed around 'a' is 'FORAGE'.
(Other definitions for forage that I've seen before include "Search widely for food" , "Look for food" , "Military raid" , "Hunt for food or provisions" , "Collect food" .)