Place where you find actors start (5)
I believe the answer is:
onset
'start' is the definition.
(both can mean the beginning of something)
'place where you find actors' is the wordplay.
I cannot really understand how this works, but
'place' could be 'set' (synonyms) and 'set' is found in the answer.
The remaining letters 'on' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
(Other definitions for onset that I've seen before include "Beginning; military attack" , "Outbreak" , "Cast stone in attack" , "First signs" , "Attack using stone" .)