Matches on Saturday will show this game (5)
I believe the answer is:
chess
'will show this game' is the definition.
'chess' can be an answer for 'game' (chess game is a kind of game). I'm not certain of the rest of the definition.
'matches on saturday' is the wordplay.
'matches' becomes 'ches' (I can't justify this - if you can you should believe this answer much more).
'on' means one lot of letters goes inside another (as in clothing 'on' a person).
'saturday' becomes 's'.
'ches' going around 's' is 'CHESS'.
(Other definitions for chess that I've seen before include "Pieces moved in this" , "activity aimed at downfall of a king" , "Ancient war game whose name may have derived for the Persian for 'king'" , "that has over thirty men on board" , "In which two bishops will participate" .)