You finally react with law being broken and howl (9)
I believe the answer is:
caterwaul
'howl' is the definition.
(I've seen this before)
'you finally react with law being broken' is the wordplay.
'finally' indicates one should take the final letters.
'with' means one lot of letters go next to another.
'being broken' indicates anagramming the letters.
The final letter of 'you' is 'u'.
'u'+'react'='ureact'
'ureact' put after 'law' is 'lawureact'.
'lawureact' with letters rearranged gives 'CATERWAUL'.
'and' acts as a link.
(Other definitions for caterwaul that I've seen before include "(Make) a yowling sound" , "shrill howl" , "howl unpleasantly" , "utter shrieks" , "Feline cry" .)