Extreme physical sports have some currency in this first part of the 21st Century. One source identifies the origin of the term with the merely dangerous activities of the 1980s: skydiving, scuba diving, surfing, rock climbing, snow skiing, water skiing, snowboarding, mountain biking, mountaineering, cave exploration, storm chasing, hang gliding, and bungee jumping.
Very little attention seems to be given to extreme intellect, a failure which I would like to begin to redress.
Some extreme intellectual sports can be understood as simple extensions of common mental activities. For example, calculus is extreme addition. Multiplication is merely advanced addition; calculus is addition run amok.
Addition itself might be considered advanced counting. There are always gradations of extremity.
I realize that just saying "calculus is extreme addition" won't resonate with readers who have no clue about what calculus is. It is not the custom for essays about extreme sports to be addressed to anyone who is not already an initiate. (There being no actual initiation procedure, or any real secrets, this vagueness is the only method available to induce the illusion of caste.) Anyone initiated into the Newtonian and Leibnizian Mysteries would immediately recognize the allusion to areas under curves and volumes of rotation. (The initiates of the earlier Bhattran Mysteries may also recognize this extreme sport.)
Probability is extreme counting. Since I already said that addition is advanced counting, you might think that probability has to be another form of extreme addition, but that isn't really true. Probability branched directly off of counting and zoomed to the uttermost exremities of the Pascalian Mysteries without losing its basis in the mental activities of 5-year-olds. That doesn't preclude extreme counting from using techniques developed in other extreme games, including calculus.
Other extreme intellectual sports consist of combinations of simple games. Systems analysis is in large part extreme outlining. Many teenagers have learned to despise making outlines. Unfortunately, many analysts haven't learned to love them. But systems analysis is more than just outlining; it also contains an element of extreme sequencing, putting things in order. So systems analysis is an extreme combination of playing with hierarchy and order.
Full-blown scientific theories are much more complex. It is possible to look for the core games within scientific theories which have been raised to some extreme.
Special relativity, for example, may be thought of as being based on extreme rate problems even though one can find other extreme games within the theory.
Biological evolution is extreme breeding. That's great for farm children and FFA alumni. Evolution also involves the task of computing which family trees die out, something which might be described as extreme subtraction. And since the processes are thought to work on multiple populations and at multiple levels, evolutionary theory uses extreme analysis. An extreme of an extreme intellectual sport: No wonder biology has come to be considered the pinnacle of the sciences.
Extreme intellectual games do not, at present, have their own television network. They do have their own journals, however. Just as with physical sports, intellectual sports have magazines dedicated to each individual game and others (like Nature and Science) which attempt to cover the entire movement.
I'd love to see high schools teach students the extreme intellectual sports. But I suppose that would require that the schools hire extreme practitioners instead of education majors.