Run wild sheep over the side (7)
I believe the answer is:
rampage
'run wild' is the definition.
(I've seen this before)
'sheep over the side' is the wordplay.
'sheep' becomes 'ram' (male sheep).
'over' means one lot of letters go next to another (in a down clue, some letters go over others).
'the side' becomes 'page' (I've seen this before).
'ram'+'page'='RAMPAGE'
(Other definitions for rampage that I've seen before include "Fury" , "Destructive spree" , "Violent disorder" , "Dash around violently" , "Rush about wildly in par game" .)