Close nettle source of stinging risks (9)
I believe the answer is:
endangers
'risks' is the definition.
(I've seen this before)
'close nettle source of stinging' is the wordplay.
'close' becomes 'end' (close can mean to end or finish).
'nettle' becomes 'anger' (I've seen this before).
'source of' says to take the initial letters.
The first letter of 'stinging' is 's'.
'end'+'anger'+'s'='ENDANGERS'
(Other definitions for endangers that I've seen before include "Risks" , "Placed in peril" , "Places in peril" , "poses a threat" , "Imperils" .)