The Capture Circle is a new item introduced in Kid Icarus: Uprising that is used as a trapping device to temporarily root enemies on the spot. However, enemies are not left vulnerable while they are stuck. It is a good idea to place this item in narrow hallways, as it is an ideal opportunity for enemies to fall into the trap.
Those who come into contact with a Capture Circle get temporarily fixed to the spot. This doesn't prevent them from attacking or dodging, however, so don't underestimate your prey when using this item!