Quite shocked by partner's lead in card game (6)
I believe the answer is:
piquet
'card game' is the definition.
(piquet is a kind of card game)
'quite shocked by partner's lead' is the wordplay.
'shocked' indicates an anagram.
'by' says to put letters next to each other.
'lead' says to take the initial letters.
The initial letter of 'partners' is 'p'.
'quite' with letters rearranged gives 'iquet'.
'iquet' after 'p' is 'PIQUET'.
'in' acts as a link.
(Other definitions for piquet that I've seen before include "Card game with 32 cards" , "Racing driver" , "patrol" , "Card-game with 32 cards" , "Card game for two" .)