Man on board thrown by deals regularly backfiring (6)
I believe the answer is:
castle
'man on board' is the definition.
(man can mean a chess piece)
'thrown by deals regularly backfiring' is the wordplay.
'thrown' becomes 'cast' (I've seen this in another clue).
'by' means one lot of letters go next to another.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'backfiring' shows that the letters should be reversed in order.
The alternate letters of 'deals' are 'el'.
'el' back-to-front is 'le'.
'cast'+'le'='CASTLE'
(Other definitions for castle that I've seen before include "Another word for chess rook" , "ancient building?" , "Fortified mansion" , "E.g. Harlech, Beaumaris, Windsor" , "a piece in the corner" .)