Maybe this will make it more understandable
In a 9-7 game which equals 16, you still don't need to spot a ball as the most balls that could be used by the players without winning is one guy has 8 and the other guys has 6 for 14 and so only one more ball is required for either of them to get and win! 15 balls.
In a 9-7 game which equals 16, you still don't need to spot a ball as the most balls that could be used by the players without winning is one guy has 8 and the other guys has 6 for 14 and so only one more ball is required for either of them to get and win! 15 balls.