[greymule]

I think that if the fence is a flat stone wall, a ball hit from the plate can't hit flush and then make it up and over. However, many fences are made of thin wooden slats or flimsy chain link. When a hard drive hits near the top, the fence may briefly "give" more than it appears and then spring back quickly so that to a person watching, the apparently magical occurs. I've seen it happen a half dozen times in SP. I suspect that a slow motion camera would catch the fence bending, the ball rising, and then the fence springing back into place in front of the ball. The "lift" may come from the ball's hitting the uneven surface just right.

Even in MLB, the tops of some of the fences give enough that the ball can hit flush and make it over.

I have also seen balls, crushed by Mikens and other WMD, that have made sharp, seemingly impossible changes of direction in mid-air.