Stay drunk with knight becoming aggressive (5)
I believe the answer is:
nasty
'aggressive' is the definition.
'stay drunk with knight' is the wordplay.
'drunk' indicates an anagram.
'with' says to put letters next to each other.
'knight' becomes 'n' (chess).
'stay' with letters rearranged gives 'asty'.
'asty' put after 'n' is 'NASTY'.
'becoming' acts as a link.
(Other definitions for nasty that I've seen before include "Highly repugnant" , "Evil" , "Highly unpleasant" , "Not nice" , "Filthy" .)