My son is 17 and plays football. Complaining of ankle hurting and pains shooting up his leg. Does he need a mri?

Needs to be examined. An examination will go along way in determining what might be the problem as well as what teats need to be performed and what can be done.
Exam first. There has been a lot of great diagnostic skill derived from years of training & practice that your physician can bring to the process of examining a patient.After an exam, the physician can decide if additional studies are necessary prior to treatment.
Maybe, but... You should have your son medically evaluated to help determine the cause of his pain. He may need an MRI, but usually Doctors start out with a physical exam, and then x-rays. Depending on the findings, your Doctor may recommend an MRI or other additional imaging procedure.