To watch a master in action, watch this video of Marco Foyot giving a class in Zanesfield, Ohio in September 2013.
The basic idea is that the boule will tend to bend in the direction that your palm ends up. So if you are a right-handed thrower—
- If you want the boule to curve to the left, your hand should finish with the thumb pointing up, into the air.
- If you want the boule to curve to the right, your hand should finish with the thumb pointing down, to the ground.
As Marco points out, making the boule curve to the right is difficult for a right-handed player, and you can see how awkward his throw looks when he does it.