Fury over pregnant participants (5)
I believe the answer is:
anger
'fury' is the definition.
(fury is intense anger)
'over pregnant participants' is the wordplay.
'over' shows that the letters should be reversed in order.
'participants' says the answer is hidden in the clue (some letters 'participating' in the clue).
'regna' can be found hidden inside 'pregnant'.
'regna' reversed gives 'ANGER'.
(Other definitions for anger that I've seen before include "Nettle" , "Hack off" , "Fire" , "Strong displeasure" , "Greatly annoy" .)