Badly violated a joint (8)
I believe the answer is:
dovetail
'a joint' is the definition.
(I know that dovetail is a type of mortise and tenon)
'badly violated' is the wordplay.
'badly' is an anagram indicator.
'violated' anagrammed gives 'DOVETAIL'.
(Other definitions for dovetail that I've seen before include "Come together" , "Violated (anag) -- mortise joint" , "Fit snugly" , "Woodworking joint" , "Joint with fan-shaped tenon" .)