Fur that's spotted upset green group (6)
I believe the answer is:
ocelot
'fur' is the definition.
(I've seen this before)
'upset green group' is the wordplay.
'upset' says the letters should be written in reverse.
'green' becomes 'eco' (abbreviation for ecological).
'group' becomes 'lot'.
'eco' backwards is 'oce'.
'oce'+'lot'='OCELOT'
'that's spotted' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for ocelot that I've seen before include "Wild cat of the Americas" , "Send animal to Cole" , "Big cat" , "Feline of South and Central America" , "Wild cat, native to Central and South America - loo etc (anag)" .)