Crazy heir, way out (7)
I believe the answer is:
haywire
'crazy' is the definition.
(I've seen this before)
'heir way out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'heir'+'way'='heirway'
'heirway' anagrammed gives 'HAYWIRE'.
(Other definitions for haywire that I've seen before include "Out of order -- erratic" , "Erratic, out of control" , "All over the shop" , "Not working properly" , "Erratic (colloq.)" .)