Shorten a game for four players (7)
I believe the answer is:
Here is my best explanation:
'shorten' is the definition.
('abridge' can be a synonym of 'shorten')
'a game for four players' is the subsidiary indication.
'game for four players' becomes 'bridge' (I've seen this before).
(Other definitions for abridge that I've seen before include "Make shorter, book say", "Crop", "Big read (anag) - shorten text", "Abbreviate, contract", "Concentrate", "Curtail", "Shorten (eg, text)", "Make short work", "cut short" and "Shorten written work".)