What Causes Swelling In Leg After An Injury?

I was snowboarding on Saturday and fell on a steel barrel that was on its side with all my weight on my leg just below my knee. It immediately swelled up the size of a tennis ball. I put ice on it and the swelling went down. On monday, my whole leg from the knee down was swollen and it's swollen today as well. There is a circle where the skin got rubbed off as well. I'm not sure what is wrong with it. Any advice?