Calf bruising is a condition in which there is localized bleeding under the skin of the calf, that is, blood leaks out of the blood vessels to the outside of the blood vessels, resulting in bruising of the calf skin. There are various causes of calf skin bruising: the first cause is trauma after collision, resulting in capillary rupture and bleeding, which leads to calf bruising, but this condition often has an obvious history of trauma and is easier for the body to detect. The second common cause is vitamin C deficiency, because when vitamin C deficiency, capillary permeability increases, the density decreases, and bleeding easily occurs, even when the minor collision, there will be bruising of the calf. The third common cause is in patients with thrombocytopenia and platelet anemia, where the hemostatic function of platelets is significantly affected due to changes in platelet number and function, and subcutaneous bleeding can also occur. Calf bruising can be seen for a variety of reasons, so it is important to understand exactly which cause is causing the calf bruising and then give the corresponding treatment.