Racket strings catgut, afterwards metal, for beginners (4)
I believe the answer is:
scam
'racket' is the definition.
(I've seen this before)
'metal for beginners' is the wordplay.
'metal' becomes 'sc' (Sc is an example).
'for beginners' becomes 'am' (I can't explain this - if you can you should believe this answer much more).
'sc'+'am'='SCAM'
'strings catgut afterwards' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for scam that I've seen before include "Rip off" , "Screw" , "A slangy swindle or fraud" , "Fraud, trick (slang)" , "Fraudulent trick or swindle" .)