Filled with rage if rule is broken (6)
I believe the answer is:
ireful
'filled with rage' is the definition.
'if rule is broken' is the wordplay.
'is broken' indicates an anagram.
'if'+'rule'='ifrule'
'ifrule' with letters rearranged gives 'IREFUL'.
(Other definitions for ireful that I've seen before include "very cross" , "Full of wrath" , "Showing resentment" , "Angry" , "mad" .)