Restraining chap, a cold fish (9)
I believe the answer is:
manacling
'restraining' is the definition.
(I've seen this before)
'chap a cold fish' is the wordplay.
'chap' becomes 'man' (chap can mean a man).
'cold fish' becomes 'cling' (I can't justify this - if you can you should believe this answer much more).
'man'+'a'+'cling'='MANACLING'
(Other definitions for manacling that I've seen before include "using restraint" , "Restraining" , "Using handcuffs" .)