Leader in hiding after cadet breaks free (6)
I believe the answer is:
detach
'free' is the definition.
(I've seen this before)
'leader in hiding after cadet breaks' is the wordplay.
'leader in' says to take the initial letters.
'after' means one lot of letters go next to another.
'breaks' indicates an anagram.
The initial letter of 'hiding' is 'h'.
'cadet' with letters rearranged gives 'detac'.
'h' put after 'detac' is 'DETACH'.
(Other definitions for detach that I've seen before include "Separate, disconnect" , "Disengage, unfasten" , "Split off" , "Break off, come away" , "free" .)