Violence King George stops in the past (5)
I believe the answer is:
aggro
'violence' is the definition.
(I have seen 'Potential violence' mean 'aggro' so perhaps 'violence' could also mean 'aggro')
'king george stops in the past' is the wordplay.
'king george' becomes 'gr' (Georgius Rex).
'stops' indicates putting letters inside.
'in the past' becomes 'ago' (synonyms).
'gr' put into 'ago' is 'AGGRO'.
(Other definitions for aggro that I've seen before include "Violence - problems" , "Aggressive, violent behaviour in short" , "Provocation (informal)" , "Difficulties (slang)" , "Hostile behaviour" .)