In cold season attorney secures revolutionary outer garment (11)
I believe the answer is:
windcheater
'outer garment' is the definition.
(windcheater is a kind of outer garment)
'in cold season attorney secures revolutionary' is the wordplay.
'in' is an insertion indicator.
'cold season' becomes 'winter' (I've seen this before).
'attorney' becomes 'DA' (District Attorney).
'secures' means one lot of letters goes inside another.
'revolutionary' becomes 'Che' (Che Guevara the Marxist revolutionary).
'da' placed around 'che' is 'dchea'.
'winter' enclosing 'dchea' is 'WINDCHEATER'.
(Other definitions for windcheater that I've seen before include "warm clothing" , "jacket" .)