Fever caught on mound (5)
I believe the answer is:
chill
'fever' is the definition.
(thesaurus)
'caught on mound' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'mound' becomes 'hill' (synonyms).
'c'+'hill'='CHILL'
(Other definitions for chill that I've seen before include "Make cold; relax" , "Refrigerate" , "nip" , "Preserve by cold" , "Make cold (or frightened)" .)