@Rockybhayia
-7.5 games means that when you add up all the total games in the match for each player, we need 8 more than our opponent to win. -7.5 means the number of games lost for our player to begin the match.
So for example if Sabalenka wins 6-2, 6-2:
6+6 = 12
2+2 = 4
12-4 = 8