Never breaking neck (5)
I believe the answer is:
nerve
'neck' is the definition.
(both can mean attitude or insolence)
'never breaking' is the wordplay.
'breaking' indicates an anagram.
'never' with letters rearranged gives 'NERVE'.
(Other definitions for nerve that I've seen before include "Impudence (colloq.)" , "Confidence" , "Sauce" , "Spunk" , "Cool courage" .)