Is it possible to play sports on my hairline fractured ankle?

Would not be smart: You may turn that hairline fracture into a full displaced fracture, requiring surgery to repair.

Wait until no pain: Depending on where the fracture is, and the degree of joint involvement, you may need to give your body 6-8 weeks to heal. Often, you can progress more quickly if you are pain free (without meds) when walking on it. Especially if you are an athlete, you would benefit from working with a physical therapist to support some of the surrounding musculature and rehabilitate ankle.

Not until: It has healed and no pain or swelling is present. You could do more damage and prevent healing if still in healing phase.