Inflammation from the bursa behind the heel known as Retrocalcaneal Bursitis. Repetitive strain or friction more than the again with the heel will cause the bursa to swell causing heel pain and tenderness, swelling and ankle stiffness. Generally associated with Achilles Tendonitis and Haglunds Deformity.   Ice. Promptly use an ice https://www.theorthopaedicandpainpractice.com/the-definitive-guide-to-diagnosing-and-treating-ankle-pain-in-singapore/