Limit those inside coach (9)
I believe the answer is:
constrain
'limit' is the definition.
(constraining is a kind of limiting)
'those inside coach' is the wordplay.
'those inside' becomes 'cons' (convicts - 'inside' can mean in prison).
'coach' becomes 'train' (both can mean to instruct a sportsperson).
'cons'+'train'='CONSTRAIN'
(Other definitions for constrain that I've seen before include "Confine, limit" , "Check" , "Lock up" , "Compel towards a course of action" , "Severely restrict" .)