Restrained catching stray, if fearful (9)
I believe the answer is:
terrified
'fearful' is the definition.
(thesaurus)
'restrained catching stray if' is the wordplay.
'restrained' becomes 'tied' (tying is a kind of restraining).
'catching' indicates putting letters inside.
'stray' becomes 'err' (synonyms).
'err'+'if'='errif'
'tied' enclosing 'errif' is 'TERRIFIED'.
(Other definitions for terrified that I've seen before include "Scared stiff" , "Greatly frightened" , "Extremely frightened" , "Panic-stricken - dire refit (anag)" .)