Hi, This really sounds like an area of traumatic ecchymosis or even a traumatic hematoma. When you applied substantial weight back onto the leg/foot that was casted, and then retracted the foot back again this almost certainly injured some of the small blood vessels about the fracture site. This actually happens more often than people think, and we usually see it after the cast is removed. The blood vessels bleed underneath the upper layers of the skin from the trauma as a lot of the muscle has probably atrophied at least to a degree and it is easier to injury these blood vessels with sudden movements like that. I start to worry if you develop numbness in the toes or foot or if the cast is starting to feel tighter, this will imply that the bruising and blood is now causing swelling and really this is the only reason I would suggest going to an Emergency Room, if numbness or tightness develop then it should get looked at. Otherwise, I do think this is safe to wait until Tuesday, I do want to give you some assurance here, as I mentioned this is not uncommon to see and is really easy to do. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. David Girardi, Internal Medicine Specialist