Prisoner's fast run in Greek hunt is fantastic (6,6)
I believe the answer is:
hunger strike
'prisoner's fast' is the definition.
(fast taken by a prisoner)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for hunger strike that I've seen before include "Non-violent protest" , "fast" , "Starvation protest" .)