I thought this might be an interesting thread to get creativity flowing. The sport can be individual or team-based. Preferably it should be one that could conceivably be played professionally.
Team Tag:
The goal of the game is to get points by tagging the opposing team's taggee. Like in volleyball, the taggee would rotate after each tag. There would be four players a side, not counting reserves. The field and its size would be up to the imagination of the teams, but the starting places for each team would be designated spots in the arena. Physical contact with other players, whether on your team or on the other team, would be prohibited and penalized. In certain zones on the field, tags could be made worth more points (to compensate for attacking being made more difficult). Five game phases of twelve minutes each.
I didn't invent it, but Futurama had a very interesting mixture of Baseball and Basketball that sounded a lot of fun. They never actually explained how it plays, though (only that baserunning was supposed to replace the need of dunking).
It actually sounds really stupid when you say it out loud.
I saw this and immediatley thought of Calvin ball! XD
Danger Ball:
Get a huge exercise ball and try to kick it as high as you can, if you knock out any of the ceiling or lightbulbs you get +10 points.
If you take out a relative or friend that happens to be nearby it's a nice extra +40 points for you.
If you get yelled at or caught by an authority you're out and the game cannot continue until all players are ready.
Competitive Flag Tag/Capture the Flag Flag Tag
Using flag football flags (Long socks stuck in pockets or belt loops are also viable) two or more teams are set into starting positions on the game field. The goal in the Competitive version is to pull both flags from every member of the opposing team until none remain with flags on their person.
Players who have both their flags removed are required to take a seat immediately upon getting both flags pulled. From that point to remain where they are with any further movement restricted, however, if a member of an opposing team comes to close they can reach out and pull that players flag aiding their own team towards victory.
The game is won when only one team still has member(s) with one or both of their flags.
Alternatively in capture the flag, one team must defend a main flag from being taken to a safe zone by the opposing team. Original rules still apply for individual players.
Brick Sports
You build time consuming sculptures and then demolish them.