Any shot that lands in any fashion, outside of perfectly flat, could be claimed to have rolled. Well, maybe not a tombstone.If you want to broaden the perspective on rollers based on the concept of "disc flying more vertical than horizontal", it would allow grenades that don't roll, and extreme height vertical backhand shots intended to get over foliage and not roll much when hitting ground. Those types of vertical shots were allowed as "rollers" at our events.