Container idiot knocked over (3)
I believe the answer is:
tin
'container' is the definition.
(tin is a kind of container)
'idiot knocked over' is the wordplay.
'idiot' becomes 'nit' (I've seen this before).
'knocked over' says the letters should be written backwards.
'nit' written backwards gives 'TIN'.
(Other definitions for tin that I've seen before include "Silver-white metal, used to make cans" , "With copper, makes bronze" , "loaf of bread" , "Cornish metal?" , "Silvery-white metallic element" .)