Exercise self-control lacking in others (5)
I believe the answer is:
train
'exercise' is the definition.
(training is a kind of exercising)
'self-control lacking in others' is the wordplay.
I cannot quite understand how this works, but
'in' is within the answer.
This explanation may well be incorrect...
(Other definitions for train that I've seen before include "Point" , "Locomotive and coaches" , "Aim < to prepare < railway carriages" , "Teach, series (of events)" , "Coach; attendants" .)