Blew his turn somewhat in card game (5)
I believe the answer is:
whist
'card game' is the definition.
(whist is a kind of card game)
'blew his turn somewhat' is the wordplay.
'somewhat' indicates a hidden word.
'WHIST' is hidden within 'blew his turn'.
'in' acts as a link.
(Other definitions for whist that I've seen before include "calls for silence?" , "Card game, often played at a "drive"" , "Old card game" , "Popular card game, sometimes solo" , "Card-game" .)