Your son needs to be seen by a spine specialist and he needs to be seen ASAP.
He needs to have an MRI to evaluate what is going on with his spine. The fact that he developed pain going down his leg, indicates that there may be disc or nerve compression or both going on.
If I chiropractor has not done any kind of x-rays before doing any kind of manipulation, then he/she is a poor one to use. Doing anything like that without knowing the specific structure of the patient's spine and not doing an MRI as well, is a very risky thing to do.
If the vertebrae have slipped or a disc is herniated, manipulation by a chiropractor can and will make the situation far worse than it already is.
Your son should be doing absolutely no sports what so ever until he is properly evaluated by a doctor who specializes in spines only. Either an orthopedic surgeon that specializes in spines or a neurosurgeon that specializes in spines.
A DO after the doctor's name is not going to be able to help you or help you properly.
Your son is far too young to be playing risky games with a back injury by continuing to play sports, use chiropractors and seeing docs with a DO attached to their name.
Get him to a spine specialist right away, it should have been done when he first injured his back.
Fran