Right-wing judge imprisons Oscar (4)
I believe the answer is:
tory
'right-wing' is the definition.
'judge imprisons oscar' is the wordplay.
'judge' becomes 'try' (as in trialling a defendant).
'imprisons' means one lot of letters goes inside another.
'oscar' becomes 'O' (phonetic alphabet: alpha, bravo, charlie etc.).
'try' going around 'o' is 'TORY'.
(Other definitions for tory that I've seen before include "type on right? Yes" , "English Conservative politician or Donegal island" , "Traditionalist" , "blue" , "Politician; tyro (anag.)" .)