Quoted from goatdan:

The rules all make sense. The right flipper button "serves" the ball into play. What doesn't make sense is that...
On a 2p game, the center shot which turns off your opponents flippers for a bit of time (awesome feature, by the way) scores the same as the opponent losing the ball. It's possible once you get halfway good at the game to shoot the ball over the center shot six times and then you can just keep letting it drain on your side to "win". It's rather silly, and the game should either give the most points to the player who does not lose the ball, or track it separately and only give the player who "wins" a score in the end.