Group chasing retreating green carnivore (6)
I believe the answer is:
ocelot
'carnivore' is the definition.
(ocelot is a kind of carnivore)
'group chasing retreating green' is the wordplay.
'group' becomes 'lot'.
'chasing' means one lot of letters go next to another (some letters chase after others).
'retreating' says the letters should be written in reverse.
'green' becomes 'eco' (abbreviation for ecological).
'eco' reversed gives 'oce'.
'lot' put after 'oce' is 'OCELOT'.
(Other definitions for ocelot that I've seen before include "Wild cat of the Americas" , "Wild cat, native to Central and South America - loo etc (anag)" , "South and Central American wildcat" , "Small leopardlike cat" , "Spotted New World feline" .)