Remainder are about to practice self-control (9)
I believe the answer is:
restraint
'self-control' is the definition.
(I've seen this before)
'remainder are about to practice' is the wordplay.
'remainder are' becomes 'rest' (I can't explain this - if you can you should believe this answer much more).
'about' is an insertion indicator.
'to practice' becomes 'train' (I've seen this in another clue).
'rest' enclosing 'train' is 'RESTRAINT'.
Can you help me to learn more?
(Other definitions for restraint that I've seen before include "Something that holds back" , "It keeps someone or something under control" , "Limiting device" , "Reserve" , "Start rain as an impediment" .)