Group of soldiers or police capturing rebel leader (5)
I believe the answer is:
corps
'group of soldiers' is the definition.
(I've seen this before)
'police capturing rebel leader' is the wordplay.
'police' becomes 'cops' (cop can informally mean a police officer).
'capturing' indicates putting letters inside.
'rebel leader' becomes 'r' (I can't explain this - if you can you should believe this answer much more).
'cops' going around 'r' is 'CORPS'.
'or' is the link.
Can you help me to learn more?
(Other definitions for corps that I've seen before include "gang" , "Army grouping" , "Military body" , "fighting group" , "Group of soldiers" .)