I would lean towards actually very defined terrain maps for competitive fighting, as location within them does matter and it stays consistent without constant referencing of previous posts for the added description by both the current participants and future ones.

For example, something such as this:

[IMG]http://i60.tinypic.com/2v0hok1.jpg[/IMG]

Dark Green is trees. Grey are stone columns about 20 feet high. Light green is obvious meadow. Dark blue is water. Light blue is open air, as this would be a floating platform. The choice of a barrier preventing knocking someone off would be an option. I'd lean towards a large diameter for the circle, such as 60-100 feet.