Bruising after a fall is not uncommon, especially when located on the knee. The additional symptom of soreness and it's delayed onset is also typical for this type of injury
. The best thing to do immediately after the fall is apply ice. You can continue this for a few hours. After that, the ice is not much use. The bruise
at that point will heal by itself over the next few days. You can resume regular activity, including running, anytime you'd like. No reason to stay off it.