Careless repairs lead first into vengeance (8)
I believe the answer is:
reprisal
'vengeance' is the definition.
(I've seen this before)
'careless repairs lead first' is the wordplay.
'careless' is an anagram indicator.
'lead first' becomes 'l' (1st letter of 'lead').
'repairs' anagrammed gives 'reprisa'.
'reprisa'+'l'='REPRISAL'
'into' acts as a link.
(Other definitions for reprisal that I've seen before include "Tit for tat" , "revenge attack" , "Counterattack" , "comeback" , "Retaliatory deed" .)