Shorten a game for four players (7)
I believe the answer is:
abridge
'shorten' is the definition.
('abridge' can be a synonym of 'shorten')
'a game for four players' is the wordplay.
'game for four players' becomes 'bridge' (I've seen this before).
'a'+'bridge'='ABRIDGE'
(Other definitions for abridge that I've seen before include "Big read (anag) - shorten text" , "Curtail" , "Shorten (eg, text)" , "Condense, summarise" , "Shorten written work" .)