My leg popped while doing the splits is the pain was horrible. what should i do?

Go to the er: If something popped and the pain is horrible, chances are you have a dislocation. When you hear a noise after a motion, in general it is not a good thing. Either a fracture or dislocation and in either case prompt reduction or spinting is required. Get a pack of ice, take a tylenol (acetaminophen) and call a friend to drive you to the nearest er. Hope this helps!