Park keeper loses head, displaying fury (5)
I believe the answer is:
anger
'fury' is the definition.
(thesaurus)
'park keeper loses head' is the wordplay.
'park keeper' becomes 'ranger' (I've seen this before).
'loses head' means to remove the first letter.
'ranger' with its first letter removed is 'ANGER'.
'displaying' is the link.
(Other definitions for anger that I've seen before include "Nettle" , "Annoyance, displeasure" , "Fire" , "Strongly annoy" , "Irk" .)