Hi there.
There's a few different ways to do this - with or without physics.
Without knowing the extent of your intentions (which is important, as certain methods may add limitations or make other things you want to do later impossible) I would presume at first that you want to know what part of the ball is hitting the wall (or something) so you can affect the ball appropriately?
One way would be to have some dummy sprites which are invisible, but are the hit areas you want to use - so you would make a sprite which represents each quarter of your circle/ball and test for hits on that. You would need to set the shape of the sprite with SetSpriteShape( iSpriteIndex, shape ) - where shape=polygon. Move those sprites the same as your actual ball so they replicate it's location.
Another more precise trick could be to use a dummy (smaller) circular sprite which can be moved around inside the other circle in a 2-pass collision check. In a way, this is a circular version of the old school per-pixel check mechanic.
If you make a circular collision check with your original ball and it passes, then you run the 2nd phase which is to see which part of the ball collided. To do this, you would rotate (and test) the smaller ball which is rotated on or around the orbit of the larger ball with some simple maths. When this hit checks, you have the angle of the ball collision, which you can use for whatever you need.
You would probably not check all 360 degrees, but whatever precision you want to follow is up to you. The size of the inner ball compared to the larger one would be relative to how many pixels your ball moved per check, so you'd always be sure of getting a 2nd pass result.
