Green coating spoiling diver's rig (9)
I believe the answer is:
verdigris
'green coating' is the definition.
'verdigris' can be an answer for 'coating' (verdigris is a kind of coating). I'm unsure of the 'green' bit.
'spoiling diver's rig' is the wordplay.
'spoiling' is an anagram indicator.
'divers'+'rig'='diversrig'
'diversrig' with letters rearranged gives 'VERDIGRIS'.
Can you help me to learn more?
(Other definitions for verdigris that I've seen before include "Green patina" , "Greenish blue coating on copper" , "oxidation" , "Greenish-blue coat on copper" , "Patina on copper" .)