Forest dweller's attack interrupting summer in retreat (3,5)
I believe the answer is:
red panda
'forest dweller's' is the definition.
(red pandas live in forests)
'attack interrupting summer in retreat' is the wordplay.
'attack' becomes 'pan' (pan can mean to attack or criticise).
'interrupting' means one lot of letters goes inside another.
'summer' becomes 'adder' (someone who adds or does sums).
'in retreat' says the letters should be written in reverse.
'adder' reversed gives 'redda'.
'pan' going inside 'redda' is 'RED PANDA'.
(Other definitions for red panda that I've seen before include "Himalayan mammal" , "Wild animal" , "furry creature" , "something like a raccoon" , "Raccoon-like mammal" .)