Explained: How does a soccer ball swerve?

It happens every four years: The World Cup begins and some of the world's most skilled players carefully line up free kicks, take aim--and shoot way over the goal. The players are all trying to bend the ball into a top corner of the goal, often over a wall of defensive players and away from the reach of a lunging goalkeeper. Yet when such shots go awry in the World Cup, a blame game usually sets in. Players, fans, and pundits all suggest that the new official tournament ball, introduced every fo...