Cast's lively reel (5)
I believe the answer is:
fling
This clue might be a double definition.
'cast's' is the first definition.
(both can mean to throw)
'lively reel' is the second definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
Can you help me to learn more?
(Other definitions for fling that I've seen before include "Throw, cast" , "Highland dance - spell of way-out behaviour" , "Throw angrily in spell of indulgent pleasure" , "Toss" , "Brief amour; throw" .)