I am not too sure why it happens but when a ball python is in the care of a new owner, it seems the first shed with the new owner is always a bad one... I had this problem for a while. I thought of it as a coincidence but it happens too often for it to be. After this shed, your BP should shed normally. I wouldn't jump to "sick ball python" right away. That would cause you unnecessary stress, bad sheds happens, whether it be on the part of the owner or the BP itself.

Get a DAMP pillow case and stick him in it for 20 minutes and place it on the warm end of the enclosure. This should loosen the shed enough for it to be pulled off.