Give us complete information on the cage--the size of the cage, the bedding, the hide boxes, the heat source and the temperatures, and the humidity.
Tell us whether you are trying to feed pinkie rats or pinkie mice (neither of which is actually appropriate for a ball python hatchling, so that could be the problem itself--they are too small. Ball python hatchlings eat fuzzy rats or hopper mice).
Tell us how often you are trying to feed the snake. Tell us whether you have disturbed the snake at all or handled it. Tell us whether you are trying to feed live or frozen/thawed.
Tell us where the cage is, and whether there is a lot of traffic nearby.
With all of that information, we may be able to make some suggestions to help you out.