Hard core once more rises and falls (7)
I believe the answer is:
niagara
'falls' is the definition.
(Niagara Falls)
'hard core once more rises' is the wordplay.
'core' indicates the central letters.
'once more' becomes 'again' (synonyms).
'rises' is a reversal indicator.
The central letters of 'hard' are 'ar'.
'ar'+'again'='aragain'
'aragain' in reverse letter order is 'NIAGARA'.
'and' acts as a link.
(Other definitions for niagara that I've seen before include "1953 Marilyn Monroe film noir thriller" , "River flowing from Lake Erie into Lake Ontario" , "US/Canadian falls" , "Famous 12" , "Famous Falls once walked by Blondin" .)