Giant to turn leg-up? (5)
I believe the answer is:
magog
'giant' is the definition.
(I've seen this before)
'turn leg-up?' is the wordplay.
'turn' becomes 'go' (a person's move in a board game).
'leg' becomes 'gam' (informal term for a woman's leg).
'up?' says the letters should be written backwards (in down clue: letters go upwards).
'go'+'gam'='gogam'
'gogam' written backwards gives 'MAGOG'.
'to' acts as a link.
(Other definitions for magog that I've seen before include "Last of two old giants" , "Biblical king" , "Gog's companion" , "old giant" , "Gog and -, City of London guardian giants" .)