Rowdy disrupting the funfair (7)
I believe the answer is:
ruffian
'rowdy' is the definition.
(I know that rowdy can be written as ruffian)
'disrupting the funfair' is the wordplay.
'disrupting' is an anagram indicator.
'funfair' with letters rearranged gives 'RUFFIAN'.
(Other definitions for ruffian that I've seen before include "Lout" , "Bully" , "Yobbo" , "Aggressive, rude troublemaker" , "Violent, lawless person" .)