Beginning of sob story, hackneyed (5)
I believe the answer is:
stale
'hackneyed' is the definition.
(thesaurus)
'beginning of sob story' is the wordplay.
'beginning of' says to take the initial letters.
'story' becomes 'tale' ('tale' can be a synonym of 'story').
The initial letter of 'sob' is 's'.
's'+'tale'='STALE'
(Other definitions for stale that I've seen before include "Unfresh" , "Musty or hackneyed" , "Lacking freshness" , "Mouldy or hackneyed" , "Old; musty" .)