Apprehend a ring-leader, then the others (6)
I believe the answer is:
arrest
'apprehend' is the definition.
('arrest' can be a synonym of 'apprehend')
'a ring-leader then the others' is the wordplay.
'leader' says to take the initial letters.
'then' is a charade indicator (letters next to each other).
'the others' becomes 'rest' (I've seen this in other clues).
The first letter of 'ring' is 'r'.
'a'+'r'+'rest'='ARREST'
(Other definitions for arrest that I've seen before include "Stop - take into custody" , "apprehend a law-breaker" , "Collar" , "Bring to a standstill" , "Nab" .)