At back, chap, snake, one not worth listening to (8)
I believe the answer is:
prattler
'one not worth listening to' is the definition.
I can't tell whether this definition defines the answer.
'at back chap snake' is the wordplay.
'at' means one lot of letters go next to another.
'back chap' becomes 'p' (I can't justify this - if you can you should believe this answer much more).
'snake' becomes 'rattler' (rattler is a kind of snake).
'p' put next to 'rattler' is 'PRATTLER'.
Can you help me to learn more?
(Other definitions for prattler that I've seen before include "One talking foolishly" , "source of gossip" , "One may go on" , "One going on" , "One talks" .)