Instruct the others outside in self-control (9)
I believe the answer is:
restraint
'self-control' is the definition.
(I've seen this in another clue)
'instruct the others outside' is the wordplay.
'instruct' becomes 'train' (training is a kind of instructing).
'the others' becomes 'rest' (other people are the rest).
'outside' is an insertion indicator.
'train' placed inside 'rest' is 'RESTRAINT'.
'in' acts as a link.
(Other definitions for restraint that I've seen before include "Self-discipline" , "Reserve" , "Control, restriction, curtailment" , "Start rain as an impediment" , "It keeps someone or something under control" .)