Indication of approval to include King in batch of playing cards (5)
I believe the answer is:
trick
'batch of playing cards' is the definition.
(term in bridge)
'indication of approval to include king' is the wordplay.
'indication of approval' becomes 'tick'.
'to include' indicates putting letters inside.
'king' becomes 'R' (abbreviation for rex, king in Latin).
'tick' enclosing 'r' is 'TRICK'.
'in' is the link.
(Other definitions for trick that I've seen before include "Hoax; knack" , "Stratagem - part of card play" , "Deceive, perhaps with cards" , "Mischievous joke" , "Sleight of hand" .)