Doctrinaire don ignored new rules (8)
I believe the answer is:
criteria
'rules' is the definition.
('criterion' can be a synonym of 'rule')
'doctrinaire don ignored new' is the wordplay.
'ignored' suggests deleting specific letters.
'new' indicates anagramming the letters.
'doctrinaire' with 'don' taken away is 'ctriaire'.
'ctriaire' anagrammed gives 'CRITERIA'.
(Other definitions for criteria that I've seen before include "Standards on which to base judgement" , "Standards for judging" , "Principles on which to base a judgement" , "Standards for assessment" , "Principles or standards by which to judge" .)