Stupid sheep rolling over by a plant (9)
I believe the answer is:
amaryllis
'plant' is the definition.
(amaryllis is a kind of plant)
'stupid sheep rolling over by a' is the wordplay.
'stupid' becomes 'silly' (I've seen this before**).
'sheep' becomes 'ram' (ram is a kind of sheep).
'rolling over' says the letters should be written in reverse.
'by' means one lot of letters go next to another.
'silly'+'ram'='sillyram'
'sillyram' in reverse letter order is 'maryllis'.
'maryllis' put after 'a' is 'AMARYLLIS'.
(Other definitions for amaryllis that I've seen before include "Trumpet-flowered bulb" , "Lily-like plant" , "Sly alarm I turn on for the flower" , "Bulbous plant with trumpet-shaped flowers" , "Showy bulbous plant" .)