Risk when fungi is pulled up (4)
I believe the answer is:
spec
'risk' is the definition.
(short for speculation)
'fungi is pulled up' is the wordplay.
'fungi' becomes 'ceps' (cep is a type of mushroom).
'is pulled up' says the letters should be written backwards.
'ceps' back-to-front is 'SPEC'.
'when' is the link.
(Other definitions for spec that I've seen before include "Minor description of detail" , "Instructions" , "on which chance is taken" , "commercial venture" , "Awkward, clumsy" .)