Side by side, move backwards secured by rope (8)
I believe the answer is:
together
'side by side' is the definition.
'move backwards secured by rope' is the wordplay.
'move' becomes 'go' (going is a kind of moving).
'backwards' says the letters should be written in reverse.
'secured by' is an insertion indicator (I've seen this in other clues).
'rope' becomes 'tether' (I've seen this before**).
'go' reversed gives 'og'.
'og' put inside 'tether' is 'TOGETHER'.
(Other definitions for together that I've seen before include "as a group" , "at the same time" , "stable" , "In combination" , "Level-headed" .)