Shy, slip off (4)
I believe the answer is:
This could be a double definition.
'shy' is the first definition.
(both can mean to throw)
'slip off' is the second definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
Can you help me to learn more?
(Other definitions for cast that I've seen before include "discarded" , "Personnel in a play" , "Complement of actors in a play" , "Discard; actors (in play)" , "Selected to play a part" .)