Reduce length of a card game (7)
I believe the answer is:
abridge
'reduce length' is the definition.
(to abridge something is to make it shorter)
'a card game' is the wordplay.
'card game' becomes 'bridge' (bridge is a kind of card game).
'a'+'bridge'='ABRIDGE'
'of' is the link.
(Other definitions for abridge that I've seen before include "Shorten by using fewer words" , "Make shorter in brigade" , "Abbreviate, shorten" , "trim" , "Make short work" .)