Breeder's top setter bites jeans - naughty dog! (7)
I believe the answer is:
basenji
'dog' is the definition.
(I know that basenji is a type of dog)
'breeder's top setter bites jeans naughty' is the wordplay.
'top' says to take the initial letters (in a down clue, the first letter is top).
'setter' becomes 'I' (the person who set this crossword).
'bites' is an insertion indicator.
'naughty' is an anagram indicator.
The first letter of 'breeders' is 'b'.
'b'+'i'='bi'
'jeans' with letters rearranged gives 'asenj'.
'bi' going around 'asenj' is 'BASENJI'.
(Other definitions for basenji that I've seen before include "Dog unable to bark" , "Smallish hunting dog" , "Small hunting dog" , "Breed of African hunting dog that rarely barks" , "Barkless dog" .)