Maybe give him more time to settle in? Other than feeding, watering, and cleaning as necessary, try not to bother him for a good month or so. Maybe he expresses his stress differently than most ball pythons, and once he settles in and feels truly secure, he won't be so bitey.

But...be prepared to accept him as he is. Enjoy him for being a feisty character, or make arrangements to find him a good home if you can't handle an aggressive snake. (No shame in that...such animals are not for everyone!)