Park keeper losing head in fury (5)
I believe the answer is:
anger
'fury' is the definition.
(fury is intense anger)
'park keeper losing head' is the wordplay.
'park keeper' becomes 'ranger' (I've seen this before).
'losing head' means to remove the first letter.
'ranger' with its initial letter taken off is 'ANGER'.
'in' acts as a link.
(Other definitions for anger that I've seen before include "Provoke annoyance" , "Deadly sin" , "Feeling of vexation" , "Fire" , "exasperation" .)