This year bow hunting a mature doe that was out of range did something like that about 4 times,i think if you have ever watched a cat bend allmost into a u shape when it is stretching that is what the deer are doing. MY GUESS IS THERE STRETCHING.
I have seen this also mostly with bucks. These young bucks may be participating in a self satisfication activity. I have read and seen the stained yellow patch on the underside of the bellies of bucks that indicate that this is an activity that is common. I can't remember the book but I certainly remember the pictures and the patch. I gues you do what you have to do after the RUT.
PaPaBob is pretty close.........actually these deer pictures were taken in the park in San Fransisco.......notice in the second pic the one buck checking out the haunches of the buck that's humped up and strutting himself........this is illegal in all towns in California except San Fransisco......in fact I understand that the mayor is going to hand out marriage certificates to anyone who wants to marry one of these fine creatures.
Those of you lucky enough to have a copy of Leonard Lee Rue III's "The Deer of North America" will be able to turn to page 312 and see a picture of a bigger buck in the same exact pose. There are several paragraphs going in to detail on the subject, but let's just say that the bucks find the need to relieve themselves if they can't find a doe to help!