Upset crazy attempt (4)
I believe the answer is:
stab
'attempt' is the definition.
(to have a stab is to attempt something)
'upset crazy' is the wordplay.
'upset' shows that the letters should be reversed in order.
'crazy' becomes 'bats' (bats can informally mean crazy).
'bats' reversed gives 'STAB'.
(Other definitions for stab that I've seen before include "Sudden sharp feeling" , "Rough guess; to knife" , "Puncture" , "Knife thrust; attempt" , "Inflict wound with knife" .)