Bad deal on metal (4)
I believe the answer is:
lead
'metal' is the definition.
(lead is a kind of metal)
'bad deal' is the wordplay.
'bad' indicates anagramming the letters.
'deal' is an anagram of 'LEAD'.
'on' is the link.
(Other definitions for lead that I've seen before include "Show the way; soft metallic element" , "Go first" , "Be in charge of, element" , "guitar accessory?" , "Be ahead of - guide" .)