Snakes haul back potentially poisonous fungus (9)
I believe the answer is:
toadstool
'potentially poisonous fungus' is the definition.
(a toadstool might be poisonous)
'snakes haul back' is the wordplay.
'snakes' becomes 'toads' (both can mean unpleasant people).
'haul' becomes 'loot' (both can mean stolen goods).
'back' shows that the letters should be reversed in order.
'loot' back-to-front is 'tool'.
'toads'+'tool'='TOADSTOOL'
(Other definitions for toadstool that I've seen before include "jack-o'-lantern?" , "Plant akin to mushroom" , "Common fungus" , "Umbrella-shaped cap on a stalk" , "that could be poisonous" .)