Zany team appearing in southern social function (9)
I believe the answer is:
screwball
'zany' is the definition.
(I've seen this before)
'team appearing in southern social function' is the wordplay.
'team' becomes 'crew' (crew is a kind of team).
'appearing in' is an insertion indicator.
'southern' becomes 's' (abbreviation).
'social function' becomes 'ball' (I've seen this before).
's'+'ball'='sball'
'crew' inserted within 'sball' is 'SCREWBALL'.
(Other definitions for screwball that I've seen before include "Zany" , "touched person" , "Freak" , "Crazy (person)" , "Crazy American" .)