Violence in the past involving King George (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')
'past involving king george' is the wordplay.
'past' becomes 'ago' (similar in meaning).
'involving' means one lot of letters goes inside another.
'king george' becomes 'gr' (Georgius Rex).
'ago' placed around 'gr' is 'AGGRO'.
'in the' acts as a link.
(Other definitions for aggro that I've seen before include "Difficulties (slang)" , "Hostile troublemaking" , "Violence - problems" , "Violent disturbance" , "belligerence" .)