Let's say I have a 10th level wizard who wants to trap himself and an enemy in an arena made of stone, could he use wall of stone to create 4 walls around him and his opponent so that they cannot leave but there are multiple squares between them and the walls. Would this allow a saving throw? Would the enemy get free movement put of the wall?
If this question isn't clear enough I'll reword it later. I'm typing from a phone right now.
You need to anchor Wall of Stone in existing stone. So normally it should be enough to simply close up the entrance to the room you are in if it is subterranean, to have an "arena" which can not be easily left.
It is possible, but difficult, to trap mobile opponents within or under a wall of stone, provided the wall is shaped so it can hold the creatures. Creatures can avoid entrapment with successful Reflex saves.
I want to believe that this line is for trapping people in extremely small spaces but I don't know.