Boy round east finds metal (4)
I believe the answer is:
lead
'metal' is the definition.
(lead is a kind of metal)
'boy round east' is the wordplay.
'boy' becomes 'lad' (informal term for boy).
'round' means one lot of letters goes inside another.
'east' becomes 'e' (abbreviation).
'lad' placed around 'e' is 'LEAD'.
'finds' acts as a link.
(Other definitions for lead that I've seen before include "Metal - van - go ahead" , "Be ahead of - guide" , ""bullets"" , "Guide; precede" , "Guide by going in front" .)