A haematoma, also known as a bruise occurs when blood leaks from a damaged blood vessel into the tissues. Bruising can occur in a wide variety of places, such as the eye, knee, head, or in the womb during pregnancy. Harmless bruising can be treated well at home. These bruises can be caused by external force, such as a fall or a blow, but they can also form at the site of a blood draw or after surgery.