Knock back Venture Sea Scout's terms (3)
I believe the answer is:
eat
'knock back' is the definition.
(I know that knock back can be written as eat)
'venture sea scout's terms' is the wordplay.
'terms' says to take the final letters (term can mean the end of something).
The final letters of 'venture sea scout' are 'EAT'.
(Other definitions for eat that I've seen before include "Corrode" , "Do cats - bats? Do bats - cats? (Alice in Wonderland)" , "Gobble up" , "Make food disappear" , "Worry" .)