Excluded group admits nothing (3,2,2)
I believe the answer is:
out of it
'excluded' is the definition.
(I've seen this before)
'group admits nothing' is the wordplay.
'group' becomes 'outfit' (outfit is a kind of group**).
'admits' is an insertion indicator.
'nothing' becomes 'o' (looks like zero - 0).
'outfit' enclosing 'o' is 'OUT OF IT'.
(Other definitions for out of it that I've seen before include "unaware of what's going on" , "Without a chance" , "Drunk < , unaware what is happening" , "is not included" , "Excluded from participation" .)