Metals causing difficulty (4)
I believe the answer is:
snag
'difficulty' is the definition.
(snag is a kind of difficulty)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for snag that I've seen before include "Unexpected drawback" , "Tear - catch" , "Stumbling block" , "Unforeseen obstacle" , "A hidden or unexpected obstacle" .)