Hi welcome to Health care magic forum.
Thanks for calling H.C.M.Forum.
Your son got hit by a football boot, a week ago. Badly bruised and swollen, it started to become yellow this week, now it bruised badly at the bottom of the shin, now swelling has gone and there is a dent.
It is a natural process of healing,the secretions of the
injury collect at the spot, and additional secretions collect at the place, and pass to the dependant part of the head , so there is the swelling. And from there it is absorbed into the blood, anfd swelling comes down.
If there is any pain or increase in the swelling you can consult a surgeon for diagnosis and treatment.
Wishing for a quick and complete recovery.
Best regards.