Board formed by setter, backing another setter's report (6)
I believe the answer is:
embark
'board' is the definition.
(embarking is a kind of boarding)
'by setter backing another setter's report' is the wordplay.
'by' says to put letters next to each other.
'setter backing' becomes 'm' (I am not sure about this - if you are sure you should believe this answer much more).
'another' becomes 'e' (I've seen this in other clues).
'setter's report' becomes 'bark' (noise or report heard from a setter dog).
'm' put after 'e' is 'em'.
'em'+'bark'='EMBARK'
'formed' acts as a link.
(Other definitions for embark that I've seen before include "get on board" , "Set out (on an enterprise)" , "Go on board ship or plane" , "Start" , "board production" .)