Rider scratches, it's announced (6)
I believe the answer is:
clause
'rider' is the definition.
(thesaurus)
'scratches it's announced' is the wordplay.
'scratches' becomes 'claws' (clawing is a kind of scratching).
'it's announced' indicates a 'sounds like' (homophone) clue.
'claws' sounds like 'CLAUSE'.
(Other definitions for clause that I've seen before include "More than a phrase and not quite a sentence" , "Group of words" , "Joker, say" , "Separate item in contract" , "Bill's article" .)