[Jon Stratis]

I think a lot of this depends on the design of the robot. If your robot is designed to fill the maximum volume specs, odds are your CG is going to be fairly high, and you're going to be more easily tipped - it might be possible to be tipped from a single, full speed, bumper-bumper hit.

On the other hand, if your robot is short, and your CG is low... it's going to take a LOT to tip your robot. The other team would need to be pretty blatant about it, most likely resulting in them pushing in you while the side of your robot is already elevated quite a bit. I would hope something that blatant would be seen as non legal contact, since it would be bumper-frame (or other components) before the robot tipped.

The whole issue with tipping is CG. Keep your CG low enough and in the right place, and you have nothing to worry about.