Just an idea...I'm not home to try it or check the specifics of each task... Tweak your particles lifespan so they 'die' while they're inside the ball. That way they won't be seen coming out of the bottom of it. Create a second particle emitter just above the surface of the ball, pointing towards the first emitter. Tweak that emitter so its particles come out at the right angles and velocity so they look like they're bouncing. Constrain the second emitter to point at the first one. The rest you'll need to do manually. Keyframe the second emitter's position so it shows up on the right part of the ball, and keyframe the first emitter so you can change the particles so they don't die too early or late (depends on how far up and down the ball is moving). You shouldn't need tons of keyframes unless the ball is on the screen for a long time or moving around wildly. This could give you a passable look of particles bouncing off of the surface of the ball.