Curt Irish cops ruined festival (6,7)
I believe the answer is:
corpus christi
'festival' is the definition.
(I've seen this before)
'curt irish cops ruined' is the wordplay.
'ruined' is an anagram indicator.
'curt'+'irish'+'cops'='curtirishcops'
'curtirishcops' with letters rearranged gives 'CORPUS CHRISTI'.
(Other definitions for corpus christi that I've seen before include "Texan city: name shared by colleges at Oxford and Cambridge" , "Oxford or Cambridge college" , "Oxbridge college" , "Church festival; Oxford college" .)