the source

Try: spofs 0,x,y

oh. I see you already have that.

It's probably a combination of SPHOME and SPROT

Another thing you could try (but I've never done it) is have the sprite animate a rotation using SPANIM

The code in this screenshot does a reasonable job of rotating it as it moves horizontally. If we had another image of the ball - with white in the center, rotation during vertical movement would look better.