At same time as card game, hosting introduction to ludo (6)
I believe the answer is:
whilst
'at same time as' is the definition.
(whilst that was going on...)
'card game hosting introduction to ludo' is the wordplay.
'card game' becomes 'whist' (whist is a kind of card game).
'hosting' indicates putting letters inside (inserted letters are welcomed in or hosted).
'introduction to' suggests taking the first letters.
The first letter of 'ludo' is 'l'.
'whist' going around 'l' is 'WHILST'.
(Other definitions for whilst that I've seen before include "At the same time, of old" , "As long as; although" , "Whereas" .)