Casts differ about being petrified (6,5)
I believe the answer is:
scared stiff
'petrified' is the definition.
(I've seen this before)
'casts differ about' is the wordplay.
'about' indicates an anagram.
'casts'+'differ'='castsdiffer'
'castsdiffer' with letters rearranged gives 'SCARED STIFF'.
'being' is the link.
(Other definitions for scared stiff that I've seen before include "Frightened to death!" , "Petrified" .)