Disabled operatic hero losing head in wild party (4)
I believe the answer is:
orgy
'wild party' is the definition.
(I've seen this before)
'disabled operatic hero losing head' is the wordplay.
'disabled operatic hero' becomes 'porgy' (opera Porgy and Bess).
'losing head' means to remove the first letter.
'porgy' with its first letter taken away is 'ORGY'.
'in' is the link.
(Other definitions for orgy that I've seen before include "Riotous revel" , "debauched scene" , "Drunken revel" , "Wild self-indulgent party" , "Frenzy; bacchanalia" .)