Sounds like fun, but I certainly agree that someone would have to be a judge, otherwise someone would say that their force field covers them with an entire sphere has a solid angle of 4 pi steradians (Just googled what degree a sphere has since a circle is 360.  Apparently 4 pi steradians is the answer.  Dunno what that means though)

A judge might say that the force field would only cover 360x180 degrees (Half circle, a dome covering you but not underneath you) since the field isnt affecting the ground, or if it pushed the ground out of the way, you would continuously fall deeper and deeper into the ground like a drill till you reach the center of the earth. 

So something that affects the ground you stand on, say something that might destroy the ground or make an earth quake would work.  This is all assuming that there is someone who will be able to say No you cant do that because...