The qualification (for this challenge) is that you have to be your own team, in essence, a one person team. Unfortunately, there is no way to enforce it, since any team can join any challenge.

There's various expressed features that have been requested in past as join limits (few I remember):

1) maximum number of active devices
2) maximum number of active members
3) a race description box, to expand on who's the target challenge participant (to get a fair / even race, where a winner is not a foregone conclusion)

If the web developer could add such finer grain pick features, 1)+2), suspect it to be not straightforward if not darn complicated, then great. The 3rd feature, a race description so captains can understand what it's about [not native English speakers], with maybe a box [yes I've read ;>], is maybe doable, without eating big time into developer time. Free text description box... who's going to moderate if those are red face in nature? Personally, if such content would appear, then the captain setting up the race has not understood what some good-natured competition is about.

BTW if the one man team joins a race where the WCG top 10 are enrolled in, great too... The more the merrier

P.S. Still looking for that Total Contribution Race summary... years, points, results. Just checked a past race, but nothing shown at top of that nature. How much did the 8th Birthday challenge aggregate?

i think there is no sense in one-man team challenges

there is a sense to add a member challenge