Getting down on all fours is not a legal guarding position. This one is just too obvious -- it's a foul on the guy on hands and knees on the floor.
The only argument here should be whether it is a common, intentional, or flagrant foul. I would lean towards the intentional myself because it was premeditated. Depending on the severity of contact it could be a flagrant.
Definitely NOT a technical foul since the ball is live and this is not "unsporting" -- it is a contact foul.
Mark -- I think this might be the first time that I have ever disagreed with you
Call the obvious -- it makes all of our lives easier!