The primary sports of a space civilization, such as that of Aquarius Ascendant, are unlikely to be the same as the ones we watch right now (for example, sports with large volumetric requirements like baseball and most codes of football are unlikely to be popular in an environment where every cubic centimeter of air has to be scrubbed, processed, and climate-controlled). In the world of ball sports, basketball is likely to be far more popular in space than field sports, since a FIBA basketball court is only 420 square meters and requires only 3 meters of vertical space plus headroom for long ball throws – it can fit relatively easily into a spaceship that can spare a 28×15 meter space on two decks). Hockey has space requirements roughly equivalent to four basketball courts, though the dimensional arrangement would be more like three basketball courts and a few fencing strips (1830 square meters – 61m x 30m; unlike basketball however, ice hockey has no vertical space requirements beyond the height of its players plus reasonable headroom for jumping).
A baseball field, however, requires over 11,000 square meters of floor space and dozens of meters in height (the speakers at the now-demolished Hubert H. Humphrey Metrodome hung about 40 meters off the field, creating a play issue as high fly balls would occasionally bounce off of them). American football requires 4,450 square meters of floor space not counting sidelines and stands, however arena versions of same generally require substantially less.
The most popular 21st Century sports in the Stellar Alliance are basketball (both full-gravity and various low- and null-gravity versions) and various forms of hockey. Association and Rugby Football are both quite popular, because they can be played with only a ball and a cleared field – Gridiron Football requires quite a bit of additional equipment and thus is generally only played on settled worlds. Baseball is an obscure legacy sport on Earth and a handful of other inner colonies; its space requirements make it prohibitive to have on most planets.
As far as organized athletics go, on most worlds, the top sporting leagues are what we would today recognize as semi-professional. While players play the game and drill at a high level, most planets simply lack the population base necessary to allow hundreds of physically-fit adults in their prime years to spend all their time playing a game or training for it. Terra, the longest-colonized human world, has started to float the idea of professional planetary sports leagues now that its population has surpassed 2 billion, as a way of reducing the participating work force now that the planet has functional and widespread automated industry taking hold.
In the world of solo sports, bike racing is quite popular (bicycles are an essential tool of transportation on most planets, with electrically-driven motorcycles being similarly popular), along with fencing and hang-gliding. Ice skating is a popular winter pastime in places that have freezing winters; roller skating runs into the “equipment required + requires certain infrastructure” issues (though on planets that have enough smooth pavement to accommodate roller skaters, it’s highly popular as well). Shooting is not a “sport” as such – people on frontier worlds rely on guns as survival tools too much to see them as mere sports equipment – but shooting competitions remain as popular as ever.
Motor sports have a somewhat shaky place in most worlds. Motor vehicles are important to getting around and people have the same kind of emotional bonds with their cars that we do in our world, and yet people are also keenly aware that automotive pollution was a major contributor to environmental problems on many homeworlds. Motorsports therefore tend to be covert and generally involve electrically-driven vehicles rather than internal combustion ones. And yes, there is a certain outlaw cachet to the less favored engine types among the working class… as always, there’s a balance between socialized and contrariness in human beings.
So sports and sportsmanship are still around but they’ve changed over the centuries, to accommodate the restrictions and unique opportunities of living in space.
Next worldbuilding post: Food, or mass entertainment?