Severs disease (or more appropriately called Calcaneal apophysitis) is a common injury to the growth plate at the back of the heel bone in children that play a lot of sport.
The growth plate at the back of the heel is located where the heel contacts the ground during walking and running. The Achilles tendon also inserts into that growth plate, so the pull from the Achilles tendon and the impact of that growth plate in the ground, it can be easy to see why in sports that Severs disease can be quite common. The pain is typically at the back, bottom and side of the heel bone, especially after sport. It can be particularly painful to squeezing of the heel bone.
An episode of PodChatLive had an in-depth discussion of calcaneal apophysitis/Severs Disease and is well worth listening to:
The management of Severs disease typically involved managing lifestyle and the loads. Physical activities and sports need to be reduced, but this can be very challenging in the child when the parents are not around. ICE, as cold therapy may be help to reduce the pain after sports activity of the pain is bad enough. A shock absorbing heel insert can often be helpful to protect the heel bone from stress and cushion it. This can also lesson the pull from the Achilles tendon on the growth plate.