Take out an average holiday insurance package and you will almost certainly find a question that asks you whether or not you intend to take part in any dangerous activities whilst you are away. The problem is, what constitutes a dangerous activity? If you are an experienced caver, for instance, you may feel that abseiling into a deep hole under a French field is a very safe activity for you, and you may be quite correct. Unfortunately if you were to have an accident after all it would cost the insurance company far more money to have you rescued from a pothole than it would cost to pick up someone with a twisted ankle who was safely on the surface! Even a game as innocent as football or cricket can result in a broken leg and this could make it completely impossible for the patient to fly back home in a conventional aircraft; the cost of an air ambulance is quite eye watering, and it would be particularly so if the insurance company refused to pay out! Every year thousands of people worldwide are stranded abroad because they have had accidents which their holiday insurance didn't cover, and they have simply not been able to raise the very considerable costs not only of hospital treatment but also of repatriation.
Fortunately there are a number of specialist insurance companies who will cover their clients against risks of injury during participation in sports; they will particularly want to know if their clients are going to get involved in known risky pursuits such as hot air ballooning, motor racing, skiing, bungee jumping etc and the premium will be calculated according to the perceived risk but the cost could be tiny in proportion to that which could be faced by an under insured person who was unfortunate enough to have an accident.