The fighting area is now much smaller than the previous arena type. 200 ft in radius, with a 100 ft in diameter platform in the center. The area between the platform and the high wall of the stands is 50 ft. There's something lying in this space other than usual sand and hard ground: water.
The water is no out of bounds, only the stands and beyond. However, the 6 ft thick platform is floating on top of water that is 30 ft deep, so the platform is bound to sway in balance whenever shifts of movement occur on its surface. Too much weight on one side can cause that side to become submerged in water for a few seconds before the balance resets itself.