Singers from church knocked back port (5)
I believe the answer is:
choir
'singers' is the definition.
(I've seen this before)
'church knocked back port' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'knocked back' says the letters should be written in reverse.
'port' becomes 'rio' (I've seen this before).
'rio' backwards is 'oir'.
'ch'+'oir'='CHOIR'
'from' is the link.
(Other definitions for choir that I've seen before include "Band of singers" , "Singers in harmony" , "Vocal group" , "Vocalists in group" , "Singing group" .)