Cot porter assembled for guard (9)
I believe the answer is:
protector
'guard' is the definition.
(thesaurus)
'cot porter assembled' is the wordplay.
'assembled' indicates anagramming the letters.
'cot'+'porter'='cotporter'
'cotporter' is an anagram of 'PROTECTOR'.
'for' acts as a link.
(Other definitions for protector that I've seen before include "Defender" , "Patron" , "Guardian; regent" , "Box at Lord's say" .)