Looks like a dog to me, it appears that the tail is wagging and blurred. I don't believe a cat would move their tail like that. Also, the structure of the legs and rear hip don't look right. Do a google image search on mountain lion and flip back and forth between the lion pics and this pic. Just doesn't look quite right to me.

But on the topic of big cats in VA, I live in VA too and a friend of mine who is not a hunter came across what he swears was a dead mountain lion on a back country road. He checked later in the day and it was gone. The reason I suspect he may have seen a dead one was because he said it had a huge head. No other cat around here would have a huge head like that.