Alrighty, here's my theory. The number 5 signifies that we will, once again, have five robots competing at once with one robot "guarding" or something. The diamond plate could either mean we will, as has been mentioned before, a circular arena, or a "king of the hill" sort of thing. It kind of looks like a manhole, but where's the fun in that? Unless, of course, there are scattered manholes to test your robots suspesion, or a raised manhole you somehow must get your grossly oversized robot on top of.

or maybe its just another ramp.
Now for the background. It kind of looks like water, and my mom said that maybe there are out of bounds areas that either are or look like water. Or they could use water jugs . . .
The possibilities are endless!