Actors I prevent from leaving reprimand (9)
I believe the answer is:
castigate
'reprimand' is the definition.
(castigating is a kind of reprimanding)
'actors i prevent from leaving' is the wordplay.
'actors' becomes 'cast' (group of actors).
'prevent from leaving' becomes 'gate' (gate can mean to confine a student to a college).
'cast'+'i'+'gate'='CASTIGATE'
(Other definitions for castigate that I've seen before include "Berate" , "Punish" , "Blast" , "Chastise - tacit sage (anag)" , "Take to task" .)