My dad has been experiencing some foot pain at the very top of his foot, in the joint where it connects with his leg. It is obviously swollen and a bit bruised. He says the pain goes away during his daily tasks, when he walks, or stands (applied pressure). But when he sits down and takes pressure off of his foot, it begins to throb with pain. "It feels like someone is just hitting it over and over with a hammer."

Can anyone tell me what the diagnosis to his problem might be?
Thanks