Monstrous female knocked back game on ship (6)
I believe the answer is:
ogress
'monstrous female' is the definition.
(I've seen this before)
'knocked back game on ship' is the wordplay.
'knocked back' is a reversal indicator.
'game' becomes 'go' (go is a kind of game).
'on' becomes 're' ('on' can be mean 'with reference to'**).
'ship' becomes 'ss'.
'go' back-to-front is 'og'.
'og'+'re'+'ss'='OGRESS'
(Other definitions for ogress that I've seen before include "Formidable woman" , "Female monster" , "man-eater" , "Scary female" , "Monstrous female" .)