A bruise on the leg indicates a bleeding condition on the skin of the leg. This is because when bleeding occurs, hemoglobin penetrates under the skin and causes bruises on the legs. There are various causes of bruises on the legs, the most common cause is caused by trauma, such as accidental bumps and bruises. Due to the action of external force on the capillaries, resulting in the rupture of capillaries, blood from the capillaries seeped out of the capillaries to the outside of the capillaries, there will be a situation of bruises on the legs. It is also caused by blood system diseases, one of the most common diseases is coagulation disorders, such as hemophilia A, hemophilia B, and patients with vascular hemophilia, where spontaneous subcutaneous bruising sometimes occurs due to coagulation disorders. If there is trauma, collision and other factors, the bruise will be more obvious. Therefore, bruises on the legs should be examined in the hematology department, and blood tests should be performed, along with coagulation routines, to find the cause.