Register fourth comedian's regressive quip - this might get their attention (6,2)
I believe the answer is:
listen up
'might get their attention' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'register fourth comedian's regressive quip' is the wordplay.
'register' becomes 'list' (listing is a kind of registering).
'fourth comedian' becomes 'e' (tth letter of 'comedian').
'regressive' says the letters should be written backwards (to regress is to go backwards).
'quip' becomes 'pun' (I've seen this in other clues).
'pun' back-to-front is 'nup'.
'list'+'e'+'nup'='LISTEN UP'
'this' is the link.
Can you help me to learn more?
(Other definitions for listen up that I've seen before include "Oyez" , "Pay attention" , "Hear this" .)