Trouble since accommodating King George (5)
I believe the answer is:
aggro
'trouble' is the definition.
(I've seen this before)
'since accommodating king george' is the wordplay.
'since' becomes 'ago' (I've seen this before).
'accommodating' is an insertion indicator.
'king george' becomes 'gr' (Georgius Rex).
'ago' going around 'gr' is 'AGGRO'.
(Other definitions for aggro that I've seen before include "Provocation (informal)" , "Belligerent trouble" , "belligerence" , "Nasty behaviour" , "Problems and difficulties" .)