Stop others following a ringleader (6)
I believe the answer is:
arrest
'stop' is the definition.
(I know that stop can be written as arrest)
'others following a ringleader' is the wordplay.
'others' becomes 'rest' (I've seen this before).
'following' means one lot of letters go next to another.
'ringleader' becomes 'r' (first letter of ring).
'a'+'r'='ar'
'rest' put after 'ar' is 'ARREST'.
(Other definitions for arrest that I've seen before include "Take into legal custody" , "Collar" , "Land next to the sea" , "Run in" , "Nab" .)