Tough seafood with starter changed (7)
I believe the answer is:
mobster
'tough' is the definition.
(both can mean a violent person)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for mobster that I've seen before include "Gangster" , "family man" , "Hoodlum" , "Mafioso" , "Member of criminal organisation" .)