Group I found in middle of winter (5)
I believe the answer is:
nonet
'group' is the definition.
'i found in middle of winter' is the wordplay.
'i' becomes 'one' ('one' can be a synonym of 'i').
'found in' is an insertion indicator.
'middle of' indicates the central letters.
The middle of 'winter' is 'nt'.
'one' inserted into 'nt' is 'NONET'.
(Other definitions for nonet that I've seen before include "Piece for nine players" , "Work for nine players" , "Group of nine musicians" , "Piece of music for nine" , "Band's" .)