Anton Moss

I never rigged or animated in Maya, but I really like that behaviour. Here's my quick attempt at implementing that behaviour so let me know if this is what you're after. In this example, I'm using abstract controls to set the max ball rotation for each foot so you can animate the max rotation, disable it by setting it to "0", or adjust the values to your taste. In the apex graph, the values are plugged into the local port on their respective transform objects - this allows access and animation to the actual footBall control even after it has been modified. I can probably set up something fancier, like an autorig component with its own menu, so you can just add it to any rig containing the reverse foot/foot autorig component. I didn't do a thorough transform check, so it might break. Let me know.

Konstantin Magnus
Here is a version using SOPs.

This is cool! Fantastic use of copernicus sdf's and the trace sop. Time to study this wrangle.

Here's my quick attempt at a solution. I'll upload another version using a more practical example when I get around to it.