Police capturing leader in rebellious group of soldiers (5)
I believe the answer is:
corps
'group of soldiers' is the definition.
(I've seen this before)
'police capturing leader in rebellious' is the wordplay.
'police' becomes 'cops' (I've seen this before).
'capturing' means one lot of letters goes inside another.
'leader in' indicates taking the first letters.
The initial letter of 'rebellious' is 'r'.
'cops' placed around 'r' is 'CORPS'.
(Other definitions for corps that I've seen before include "Army unit" , "Specialised mil. body" , "Part of an army" , "fighting group" , "Army division" .)