UK, with Romans in disarray, goes wild (4,4)
I believe the answer is:
runs amok
'goes wild' is the definition.
'uk with romans in disarray' is the wordplay.
'with' is a charade indicator (letters next to each other).
'in disarray' indicates an anagram.
'uk'+'romans'='ukromans'
'ukromans' with letters rearranged gives 'RUNS AMOK'.
(Other definitions for runs amok that I've seen before include "Attacks people violently and without discrimination" , "Goes crazy" , "riots" , "Loses control" .)