Attempt is crazy? The reverse (4)
I believe the answer is:
stab
'attempt' is the definition.
(to have a stab is to attempt something)
'crazy? the reverse' is the wordplay.
'crazy?' becomes 'bats' (bats can informally mean crazy).
'the reverse' says the letters should be written backwards.
'bats' reversed gives 'STAB'.
'is' is the link.
(Other definitions for stab that I've seen before include "Injure with knife" , "Jab" , "Thrust at and pierce" , "Pierce with a dagger" , "shot in the dark?" .)