Celebration: a wild, crazy one (6)
I believe the answer is:
diwali
'celebration' is the definition.
(Hindu festival)
'a wild crazy one' is the wordplay.
'crazy' indicates anagramming the letters.
'one' becomes 'i' (Roman numeral).
'a'+'wild'='awild'
'awild' anagrammed gives 'diwal'.
'diwal'+'i'='DIWALI'
(Other definitions for diwali that I've seen before include "Festival in honour of Lakshmi" , "Light festival" , "Hindu festival; I'd wail (anag.)" , "religious festival" , "Indian festival" .)