There are no hard and fast rules about returning to sports after back surgery. Every surgeon looks at each patient separately. Some of the factors the doctor looks at include the patient's age, the amount and kind of surgery, and how long ago the surgery was done.
One other important part of this decision is the kind of sport or activity in question. Contact or collision sports are not advised at all for the first year after surgery. These include wrestling, gymnastics, basketball, football, and ice hockey. Many doctors advise against these kinds of activities for life.
Noncontact, low-impact activities are generally allowed after six months. These include swimming, cross country skiing, tennis, and running. Returning to gym class at school usually happens somewhere between six months and one year.