Both of my balls when I first got them (i got them both less around 3-4 months old) did bite the wrong end of a mouse at one point and got bit back. The skin broke on one but did not bleed and the other didnt even break the skin. Since then neither have been bit.

On the other hand my old roommate (who thought he was an expert with reptiles) fed his 4 ft ball one large rat a month. On more than one occasion he went 2 months without feeding it and thought it was super hungry so he gave him 2 large rats at the same time. He NEVER once at the 2nd rat but I think he did this at least 4 times. One time he left the extra rat in overnight and when he checked on the snake 2 very large portions of its back had been eaten. I didnt know him at the time, Ive only seen the massive ugly scars. He didnt try to treat it or take it to the vet, just left it alone to heal. Im suprised this only happened once. Anyways the snake has now passed do to improper care (no heat, he thought fluorescent light was enough, no humidity, he figured since it was from africa why should it need humidity). I dont talk to him anymore but I hope he doesnt get one again.