Why is my dog pooping in his crate?

i recently got a small terrier mix puppy, and at first it was fine with living in it's crate uring crate training, but for the past few days, he has began relieving himself inside of it. The weird thing is that he will relieve himself in the exact spot I set his food bowls down at. He is taken out regularly, and he knows to use the bathroom outside, and has never had any problems with his since a few days ago. He hit his head on the door a few times, so I would like to know if somehow he became crazy or dysfunctional. He will still use the bathroom outside, and he goes out every few hours, so I don't understand why he will just go to the bathroom where he eats and sleeps. He also will not relieve himself in his crate overnight, only during the day, which really confuses me. Please somebody tell me what to do, or if he is brain damaged, or if this just normal?