Called around six? That’s crazy! (6)
I believe the answer is:
raving
'crazy' is the definition.
(thesaurus)
'called around six?' is the wordplay.
'called' becomes 'rang' ('ring' can be a synonym of 'call').
'around' is an insertion indicator.
'six?' becomes 'vi' (roman numeral).
'rang' placed around 'vi' is 'RAVING'.
'that's' acts as a link.
(Other definitions for raving that I've seen before include "Mad" , "Declaiming wildly" , "Wildly incoherent" .)