Be the best in heavy metal (4)
I believe the answer is:
lead
This clue could be a double definition.
'be the best' is the first definition.
'lead' can be an answer for 'be' (leading is a kind of being). I'm not sure about the 'the best' bit.
'heavy metal' is the second definition.
(lead is a heavy metal)
'in' acts as a link.
Can you help me to learn more?
(Other definitions for lead that I've seen before include "Live" , "shot maybe" , "pioneer" , "Go ahead; element" , "Be ahead of - guide" .)