Protective cover idiot's pulled back (4)
I believe the answer is:
tarp
'protective cover' is the definition.
(short for 'tarpaulin')
'idiot's pulled back' is the wordplay.
'idiot' becomes 'prat' (I've seen this before).
'pulled back' says the letters should be written backwards.
'prat' backwards is 'TARP'.
(Other definitions for tarp that I've seen before include "Cover" , "canvas sheet" , "Bail-out" .)