Odd problem with photo - 1D MK III

I've never seen anything like this. The top half of the photo is sharp and clear while the bottom half is blurred. This photo was taken the first weekend that I had this camera. I haven't noticed this on any other photos. Has anyone else seen this before?

Thanks...

(1DMKIII, lens: 70-200 f/2.8 photo taken at ISO 200, f/4, 1/3200)

To me, it appears to be either:

1) a bad smudge at one end or another on your lens
2) a smudge on your sensor
3) badly aligned lens element
4) something obstructing your line of sight from lens to subject on the lower half of the frame, and is diffracting that part of the shot

If you don't have this on any other photo then or since, I say #4

Looks like you caught the very top of the arena glass at the very bottom of the frame.

This is the only photo where I've noticed this problem. I was shooting from the penalty box and there is no glass in that area. It is possible that the lower part of the lens was partially obstructed by something - perhaps the something on the top of the boards.

I hadn't considered that possibility because it almost appears as if there is ghosting of the logo on the breezers. Taking a second look, it could be diffraction.

Thanks.