Make fun of a disheartened jester (4)
I believe the answer is:
jeer
'make fun of' is the definition.
(thesaurus)
'a disheartened jester' is the wordplay.
'a disheartened' suggests removing the centre (the middle or heart is removed).
'jester' with its middle removed is 'JEER'.
(Other definitions for jeer that I've seen before include "Scoff, deride, mock" , "Boo" , "Rudely mocking remark" , "Taunt" , "Ridicule noisily" .)