Poor in Knock denied pence (3)
I believe the answer is:
bum
'poor' is the definition.
(both can mean poor quality)
'knock denied pence' is the wordplay.
'knock' becomes 'bump' (synonyms).
'denied' suggests deleting specific letters (the word is denied some of its letters).
'pence' becomes 'p'.
'bump' with 'p' taken away is 'BUM'.
'in' acts as a link.
(Other definitions for bum that I've seen before include "American hobo or vulgar backside" , "US tramp" , "Cadge" , "Behind" , "False" .)